I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate? If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

It's many moons since I last charged a car battery and at that time I
just clamped the charger leads on and let it get on with it.

--
F

On 08/02/2018 11:53, F wrote:

It's many moons since I last charged a car battery and at that time I
just clamped the charger leads on and let it get on with it.


That's what I do.

On Thu, 8 Feb 2018 11:53:05 +0000, F news@nowhere wrote:

I've SORNed my car as I'm not going to be able to drive it for a couple
of months.

I often don't touch the kitcar (or several motorbikes) for many months
and they all normally start ok ... so it very much depends on the
parastatic load.

No doubt the battery will eventually need a charge

*Eventually* yes. ;-)

but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate?

If you do then you can probably guarantee (depending on the state of
charge of battery on disconnection and it's general condition) it
should be ok when needed next.

If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

Radio code, what else OOI?

It's many moons since I last charged a car battery and at that time I
just clamped the charger leads on and let it get on with it.

If the car has a reasonable parastatic load (alarm etc) you will need
to do something so what you do (charge as is or with the battery
disconnected) is down to how easy it is to reset said 'electronics'?

Cheers, T i m

On Thu, 08 Feb 2018 12:28:16 +0000, T i m wrote:

On Thu, 8 Feb 2018 11:53:05 +0000, F news@nowhere wrote:

I've SORNed my car as I'm not going to be able to drive it for a couple
of months.

I often don't touch the kitcar (or several motorbikes) for many months
and they all normally start ok ... so it very much depends on the
parastatic load.

Sorry, 'parasitic' ...

Cheers, T i m

Huge wrote:

the reason people suggest disconnecting the
battery is that most modern cars have a substantial current drain even
when switched off (I've measured it at several hundred milliamperes).

Though they do progressively shutdown more and more systems over the
course of hours/days/weeks.

On 08/02/2018 11:53, F wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate? If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

It's many moons since I last charged a car battery and at that time I
just clamped the charger leads on and let it get on with it.

With a decent, modern, well-regulated charger, it isn't an issue. With
an old, poorly regulated, poorly rectified one I'd be more cautious.

CTEK ones are great, and designed to be used like this, and you can get
leads you permanently connect to the car that end in a socket that mates
with the charger; I regularly charge the battery on my other half's car
like this (she doesn't use it much).

On 08/02/2018 12:26, Huge wrote:
On 2018-02-08, Huge wrote:
On 2018-02-08, F news@nowhere wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate?

P.S. re-reading your posting, the reason people suggest disconnecting the
battery is that most modern cars have a substantial current drain even
when switched off (I've measured it at several hundred milliamperes). This
will rapidly flatten and then ruin a car battery. Which is why I use a
float/trickle charger (sometimes called a "battery conditioner").

No. My 'race' car sits for months in the garage with its battery connected
to the car and a 'el cheapo' float charger from eBay. The latter was an
experiment, following the 'el expensivo' float charger (an AirFlow one,
IIRC) that went mad and boiled the lawn mower battery dry. Asking around,
lots of other people recommended other expensive chargers, for prices
that I thought were nonsense (£50+), so I bought 2 of these;

https://www.ebay.co.uk/itm/182929657441

The car's been on one of them for 3 months now, and has been fine. The
other one awaits me buying a new lawn mower battery.



That's exactly what I would have suggested, always assuming you have
mains accessible to the parking place. If not, remove battery and either
leave it on a trickle charger, or on an ordinary one for a few hours
every month or so.

In article ,
F news@nowhere wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate? If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

With a half decent modern ordinary charger, just leave the battery
connected.
The problem can occur with a commercial fast charger - the type that can
start a car with a flat battery immediately. Which might chuck out enough
volts to damage electronics.

I have one of those excellent 13 quid Lidl chargers installed in the old
car and hard wired to a fusebox. With a waterproof mains connector under
the bumper. Allowing the battery to be charged with the car still secure.

--
*Kill one man and you're a murderer, kill a million youand 're a conqueror.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Huge wrote:
P.S. re-reading your posting, the reason people suggest disconnecting the
battery is that most modern cars have a substantial current drain even
when switched off (I've measured it at several hundred milliamperes). This
will rapidly flatten and then ruin a car battery. Which is why I use a
float/trickle charger (sometimes called a "battery conditioner").

If you take a fairly normal (large) 75 amp hour battery, a drain of 1 amp
would flatten it in 3 days. Pro rata for a lower current. And it would
fail to start before the battery was totally flat.

Most cars can last about 3 weeks without being run. Which would suggest a
quiescent current draw of rather under 100mA. But it may be higher until
the electrics finally go to sleep.

--
*Do they ever shut up on your planet?

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
T i m wrote:
On Thu, 08 Feb 2018 12:28:16 +0000, T i m wrote:

On Thu, 8 Feb 2018 11:53:05 +0000, F news@nowhere wrote:

I've SORNed my car as I'm not going to be able to drive it for a couple
of months.

I often don't touch the kitcar (or several motorbikes) for many months
and they all normally start ok ... so it very much depends on the
parastatic load.

Sorry, 'parasitic' ...

Quiescent. It is necessary ;-)

--
*How can I miss you if you won't go away?

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Chris Bartram wrote:
With a decent, modern, well-regulated charger, it isn't an issue. With
an old, poorly regulated, poorly rectified one I'd be more cautious.

Assuming the battery isn't knackered, the internal impedance will stop
most chargers doing anything silly. Excepting a very powerful garage type
one.

--
*This message has been ROT-13 encrypted twice for extra security *

Dave Plowman London SW
To e-mail, change noise into sound.

On Thu, 08 Feb 2018 12:23:15 +0000, Huge wrote:

On 2018-02-08, F news@nowhere wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate?

No. My 'race' car sits for months in the garage with its battery
connected to the car and a 'el cheapo' float charger from eBay. The
latter was an experiment, following the 'el expensivo' float charger (an
AirFlow one, IIRC) that went mad and boiled the lawn mower battery dry.
Asking around, lots of other people recommended other expensive
chargers, for prices that I thought were nonsense (£50+), so I bought 2
of these;

https://www.ebay.co.uk/itm/182929657441

The car's been on one of them for 3 months now, and has been fine. The
other one awaits me buying a new lawn mower battery.

You need to be aware that SLI LA batteries aren't designed to cope with
continuous float charging for month after month after month periods at
the classic (and seemingly more benign) 13.8v level. Six months seemed to
be the point where such 'gentle float charging' would ruin them (a bunch
of four connected to an APC SmartUPS2000 2KVA/1500W rated UPS... Twice!).

Another problem is the lack of stirring of the electrolyte to prevent
stratification. Surprisingly, the apparently rough treatment meted out by
the alternator's 14.0 to 14.2 float charging and the vibrations and
accelerations of a moving vehicle all conspire to maintain the battery in
peak condition. The high voltage 'float charging' under these normal
conditions of use, rarely top more than 3 or 4 hours per day, unlike the
unremitting regime of a permanently connected 13.8v battery charger.

You really only need to stop the battery voltage dipping below the 12.7v
mark so a basic 13.8v constant voltage charger can be used with a 6A or
higher rated silicon diode to drop the charging voltage down to the 13.1v
mark if you can't get hold of a 13.5v constant voltage charger.

Alternatively, a "Smart charger" that can boost the battery voltage to
14v for half an hour every 24 hours that just monitors the battery
voltage during the other 23.5 hours of the day to make sure it doesn't
drop below 12.6v in between these brief bursts of freshening charges is
probably the best you can do to maintain the battery in a healthy state.

You won't be able to prevent stratification of the electrolyte unless
you're prepared to remove the battery onto a stirring platform or else
are prepared to set the burst charge rate to 15 or 16 volts to induce
gassing and the need to top up with distilled water every other week or
so.

Probably the simplest "Fit 'n' Forget" solution is to use a standard
13.8v charger designed to maintain SLA batteries which can tolerate this
constant voltage float charging regimen (even better if 13.5v is used)
with a simple silicon diode volt dropper to hold the battery at a
constant 13.1v for the duration.

An alternatively "Cheap 'n' Cheerful" solution, if you already have a
simple unregulated transformer/rectifier battery charger to hand, is to
invest in a basic mechanical timer switch to put in line with the old
fashioned charger set up to give it half an hour per day's boosting
charge. The important point in all of this, being the avoidance of an
unrelenting 13.8v float charging regime over a period of 5 or more months
at a time.

--
Johnny B Good

"Dave Plowman (News)" wrote in message
...
In article ,
F news@nowhere wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate? If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

With a half decent modern ordinary charger, just leave the battery
connected.
The problem can occur with a commercial fast charger - the type that can
start a car with a flat battery immediately. Which might chuck out enough
volts to damage electronics.

I have one of those excellent 13 quid Lidl chargers installed in the old
car and hard wired to a fusebox. With a waterproof mains connector under
the bumper. Allowing the battery to be charged with the car still secure.


And they are on sale again in Lidl today



-

Can you not trickle charge it for a few hours a day on a cheapo timer? You
are right its probably going to be very very flat and also I feel that
vehicles engines should be turned over pretty regularly as well.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"F" news@nowhere wrote in message
...
I've SORNed my car as I'm not going to be able to drive it for a couple of
months. No doubt the battery will eventually need a charge but do I really
have to disconnect it as current [pun not intended] advice seems to
indicate? If I do, I will, no doubt, have a whole lot of setting up to do
on the various electronics.

It's many moons since I last charged a car battery and at that time I just
clamped the charger leads on and let it get on with it.

--
F

In article , Dave Plowman (News)
wrote:
In article , Huge
wrote:
P.S. re-reading your posting, the reason people suggest disconnecting
the battery is that most modern cars have a substantial current drain
even when switched off (I've measured it at several hundred
milliamperes). This will rapidly flatten and then ruin a car battery.
Which is why I use a float/trickle charger (sometimes called a "battery
conditioner").

If you take a fairly normal (large) 75 amp hour battery, a drain of 1 amp
would flatten it in 3 days. Pro rata for a lower current. And it would
fail to start before the battery was totally flat.

Most cars can last about 3 weeks without being run. Which would suggest a
quiescent current draw of rather under 100mA. But it may be higher until
the electrics finally go to sleep.

The main source of current drain is probably the radio. When you switch it
off, you're only turning off the amplifier, the tuning bits, etc, are still
powered. Alarms also take a bit of power.

--
from KT24 in Surrey, England

On Thu, 08 Feb 2018 14:23:04 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
T i m wrote:
On Thu, 08 Feb 2018 12:28:16 +0000, T i m wrote:

On Thu, 8 Feb 2018 11:53:05 +0000, F news@nowhere wrote:

I've SORNed my car as I'm not going to be able to drive it for a couple
of months.

I often don't touch the kitcar (or several motorbikes) for many months
and they all normally start ok ... so it very much depends on the
parastatic load.

Sorry, 'parasitic' ...

Quiescent. It is necessary ;-)

Good point ... assuming it is actually being used (like an alarm as
I'm assuming an immobiliser would still be 'working' anyway? ). ;-)

Cheers, T i m

In article ,
charles wrote:
In article , Dave Plowman (News)
wrote:
In article , Huge
wrote:
P.S. re-reading your posting, the reason people suggest
disconnecting the battery is that most modern cars have a
substantial current drain even when switched off (I've measured it
at several hundred milliamperes). This will rapidly flatten and then
ruin a car battery. Which is why I use a float/trickle charger
(sometimes called a "battery conditioner").

If you take a fairly normal (large) 75 amp hour battery, a drain of 1
amp would flatten it in 3 days. Pro rata for a lower current. And it
would fail to start before the battery was totally flat.

Most cars can last about 3 weeks without being run. Which would
suggest a quiescent current draw of rather under 100mA. But it may be
higher until the electrics finally go to sleep.

The main source of current drain is probably the radio. When you switch
it off, you're only turning off the amplifier, the tuning bits, etc, are
still powered. Alarms also take a bit of power.

On a modern car you might be amazed how much is powered up all the time.
My radio retains its station memory etc even if totally powered down.

--
*I couldn't repair your brakes, so I made your horn louder *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
T i m wrote:
On Thu, 08 Feb 2018 14:23:04 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
T i m wrote:
On Thu, 08 Feb 2018 12:28:16 +0000, T i m wrote:

On Thu, 8 Feb 2018 11:53:05 +0000, F news@nowhere wrote:

I've SORNed my car as I'm not going to be able to drive it for a couple
of months.

I often don't touch the kitcar (or several motorbikes) for many months
and they all normally start ok ... so it very much depends on the
parastatic load.

Sorry, 'parasitic' ...

Quiescent. It is necessary ;-)

Good point ... assuming it is actually being used (like an alarm as
I'm assuming an immobiliser would still be 'working' anyway? ). ;-)

Don't forget the remote central locking. Requires a receiver of some sort
powered up at all times. Then there's likely one of those nice units that
fade the interior lights up and down when you open a door. Same sort of
thing.

--
*It is easier to get older than it is to get wiser.

Dave Plowman London SW
To e-mail, change noise into sound.

On 08/02/2018 14:22, Dave Plowman (News) wrote:

If you take a fairly normal (large) 75 amp hour battery, a drain of 1 amp
would flatten it in 3 days.

No. Two days at most. You never get 75Ah out of a 75Ah battery.

Bill

On 08/02/2018 11:53, F wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate? If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

It's many moons since I last charged a car battery and at that time I
just clamped the charger leads on and let it get on with it.



Why not start it once a week, give it a good revving then let it tick
over for ten minutes? That will stir the battery electrolyte a bit and
also keep the engine happy. Move it backwards and forwards a bit so the
clutch and brakes don't rust up.

If your only concern is the battery you could follow my method, which is
to have the charger powered from a circuit that is only on occasionally.
In my case it's the power to an outbuilding, which might be on for half
an hour a week.

Bill

"Dave Plowman (News)" wrote:

On a modern car you might be amazed how much is powered up all the time.
My radio retains its station memory etc even if totally powered down.

Which doesn't actually need any power, flash memory retains its
contents with no power. Older radios used to use powered memory to
retain things but I'm not sure that modern ones do.

--
Chris Green
·

On Thursday, 8 February 2018 19:03:05 UTC, Chris Green wrote:
"Dave Plowman (News)" wrote:

On a modern car you might be amazed how much is powered up all the time.
My radio retains its station memory etc even if totally powered down.

Which doesn't actually need any power, flash memory retains its
contents with no power. Older radios used to use powered memory to
retain things but I'm not sure that modern ones do.

Older ones didn't have memories, they had valves. And at least some proudly declared 'transistor' on the front regardless.


NT

F submitted this idea :
I've SORNed my car as I'm not going to be able to drive it for a couple of
months. No doubt the battery will eventually need a charge but do I really
have to disconnect it as current [pun not intended] advice seems to indicate?
If I do, I will, no doubt, have a whole lot of setting up to do on the
various electronics.

It's many moons since I last charged a car battery and at that time I just
clamped the charger leads on and let it get on with it.

If the charger is a modern controlled charger, no problem - just
connect and charge despite the warnings. I would not leave it
permanently on charge, even though the charger instructions might
suggest you can do this. Initially bring it to a fully charged
condition, maybe 24 hours, then every month or so repeat. That assumes
that your car has no major sources of discharge/faults - It should
discharge at less than 50mA-ish, depending on the model and its age.

Huge explained :
(I've measured it at several hundred milliamperes).

At that level of discharge, I would suggest the vehicle has a fault -
something is not properly going into sleep mode and the reason needs to
be investigated.

charles explained on 08/02/2018 :
The main source of current drain is probably the radio. When you switch it
off, you're only turning off the amplifier, the tuning bits, etc, are still
powered. Alarms also take a bit of power.

Wrong - only the memories and clock are maintained with power off, a
matter of uA or a mA or so. My own car which is packed with maintained
electronics, satnav, TV and radio plus an alarm system, only draws 20ma
when in sleep mode after 1 minute.

on 08/02/2018, Johnny B Good supposed :
You need to be aware that SLI LA batteries aren't designed to cope with
continuous float charging for month after month after month periods at
the classic (and seemingly more benign) 13.8v level. Six months seemed to
be the point where such 'gentle float charging' would ruin them (a bunch
of four connected to an APC SmartUPS2000 2KVA/1500W rated UPS... Twice!).

You are spot on with that. I have several such batteries and having
wrecked a few in the past, by using 13.8v 'maintenance' chargers, my
regime now is one of bringing them up to a full charge once every 1 or
2 months. The diodes trick will only work, where the charger will
charge irrespective of seeing a voltage across its output.

Dave Plowman (News) laid this down on his screen :
Assuming the battery isn't knackered, the internal impedance will stop
most chargers doing anything silly. Excepting a very powerful garage type
one.

Even an old fashioned transformer, rectifier - raw DC of stated 4amp
output is more than capable of wrecking a perfectly good battery, if
left on charge. I know, I have done it.

on 08/02/2018, Dave Plowman (News) supposed :
Don't forget the remote central locking. Requires a receiver of some sort
powered up at all times. Then there's likely one of those nice units that
fade the interior lights up and down when you open a door. Same sort of
thing.

Modern ones, draw micro-amps. All of that wakes up when a signal is
received, otherwise asleep for the most part.

On 08/02/2018 11:53, F wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate? If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

It's many moons since I last charged a car battery and at that time I
just clamped the charger leads on and let it get on with it.

Thanks, all!

I'll clamp the leads on with the battery still connected and put the
charger on a timer to top it up for 30 minutes a day.

Sounds like a plan?

As for the rusting brakes issue, it's in the garage, I've left the
handbrake off, and I've put a brick behind the rear wheel to stop it
moving and jamming the garage door.

The clutch might need to gather a little rust as I expect my
soon-to-be-replaced knee won't like exercising the clutch pedal for some
times.

--
F

On 08/02/2018 18:23, Bill Wright wrote:
On 08/02/2018 14:22, Dave Plowman (News) wrote:

If you take a fairly normal (large) 75 amp hour battery, a drain of 1 amp
would flatten it in 3 days.

No. Two days at most. You never get 75Ah out of a 75Ah battery.

Bill


75ahr at what rate?
Low rate discharge usually gets far more energy out of the battery than
the 20hr rate and a hell of a lot more than cold starting a diesel engine.

On Thu, 8 Feb 2018 20:33:15 +0000, F news@nowhere wrote:

On 08/02/2018 11:53, F wrote:
I've SORNed my car as I'm not going to be able to drive it for a couple
of months. No doubt the battery will eventually need a charge but do I
really have to disconnect it as current [pun not intended] advice seems
to indicate? If I do, I will, no doubt, have a whole lot of setting up
to do on the various electronics.

It's many moons since I last charged a car battery and at that time I
just clamped the charger leads on and let it get on with it.

Thanks, all!

I'll clamp the leads on with the battery still connected and put the
charger on a timer to top it up for 30 minutes a day.

Sounds like a plan?

I'd say, if you can't get a timer to turn it on once a week (what car
can't be left a week with no issues)?

If you had a DMM I'd just monitor it the first time and watch the
voltage (and / or current) to see if both 'flatten out'. If they do
then your on time was sufficient.

As for the rusting brakes issue, it's in the garage, I've left the
handbrake off, and I've put a brick behind the rear wheel to stop it
moving and jamming the garage door.

Good idea.

The clutch might need to gather a little rust as I expect my
soon-to-be-replaced knee won't like exercising the clutch pedal for some
times.

My kitcar clutch is currently seized on and my std release process is
to first start it and get the engine warm then once warm, stop the
engine, put it in first and start it again and with the clutch fully
depressed then 'kangaroo' it on the throttle ... that usually does it.
(If I can't get it to release with the handbrake on and in first, just
using the starter motor).

Given it's a cable clutch I was wondering if it should be left with
some pressure on the clutch pedal, maybe just enough to get the clutch
to separate from the flywheel and pressure plate 'slightly'?

Cheers, T i m

In article , Andy Burns
writes
Huge wrote:

the reason people suggest disconnecting the
battery is that most modern cars have a substantial current drain even
when switched off (I've measured it at several hundred milliamperes).

Though they do progressively shutdown more and more systems over the
course of hours/days/weeks.

But they will still flatten the battery.
--
bert

In article ,
writes
On Thursday, 8 February 2018 19:03:05 UTC, Chris Green wrote:
"Dave Plowman (News)" wrote:

On a modern car you might be amazed how much is powered up all the time.
My radio retains its station memory etc even if totally powered down.

Which doesn't actually need any power, flash memory retains its
contents with no power. Older radios used to use powered memory to
retain things but I'm not sure that modern ones do.

Older ones didn't have memories, they had valves. And at least some
proudly declared 'transistor' on the front regardless.


NT
They're not older, they're ancient
--
bert

In article ,
bert wrote:
In article , Andy Burns
writes
Huge wrote:

the reason people suggest disconnecting the
battery is that most modern cars have a substantial current drain even
when switched off (I've measured it at several hundred milliamperes).

Though they do progressively shutdown more and more systems over the
course of hours/days/weeks.

But they will still flatten the battery.

my Citroen C5 used to warn that the battery was getting low and certain
functions would be switched off,

--
from KT24 in Surrey, England

On Thu, 8 Feb 2018 22:05:48 +0000, bert wrote:

In article ,
writes
On Thursday, 8 February 2018 19:03:05 UTC, Chris Green wrote:
"Dave Plowman (News)" wrote:

On a modern car you might be amazed how much is powered up all the time.
My radio retains its station memory etc even if totally powered down.

Which doesn't actually need any power, flash memory retains its
contents with no power. Older radios used to use powered memory to
retain things but I'm not sure that modern ones do.

Older ones didn't have memories, they had valves. And at least some
proudly declared 'transistor' on the front regardless.


NT
They're not older, they're ancient

Spoken by someone no doubt that thinks a vibrator was something that
came from Anne Summers :-)

[Not the best thing for long wave incidentally]

AB

On Thu, 08 Feb 2018 22:34:04 +0000, Archibald Tarquin Blenkinsopp wrote:

Spoken by someone no doubt that thinks a vibrator was something that
came from Anne Summers

God, I'd forgotten about those.
--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On 08/02/2018 20:48, Huge wrote:
On 2018-02-08, Andy Burns wrote:
Huge wrote:

the reason people suggest disconnecting the
battery is that most modern cars have a substantial current drain even
when switched off (I've measured it at several hundred milliamperes).

Though they do progressively shutdown more and more systems over the
course of hours/days/weeks.

Some of them do. Not all.

I remember driving a car where the alternator was not charging the
battery, as the journey went on "it" kept dropping services[1] until
finally the car conked out alltogether. From first symptoms to conking
out was twenty~thirty minutes minutes (ten or so miles).
Livingston going back to Edinburgh, knew there was a problem but wanted
to get son(special needs) home or at least as close as possible.

[1] First the radio, then the power steering, then the speedo. Was
'great fun on the A71 with no power steering . My speed awareness is
crap, without a speedo, cars were queueing up behind me. Mind you didn't
want to go too fast with things stopping working .

In article ,
Chris Green wrote:
"Dave Plowman (News)" wrote:

On a modern car you might be amazed how much is powered up all the
time. My radio retains its station memory etc even if totally powered
down.

Which doesn't actually need any power, flash memory retains its
contents with no power. Older radios used to use powered memory to
retain things but I'm not sure that modern ones do.

Yes. But that has been replaced by all the other things that take power at
all times. Maybe only a small amount each - but it adds up.

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Dave Plowman London SW
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In article ,
Harry Bloomfield wrote:
Dave Plowman (News) laid this down on his screen :
Assuming the battery isn't knackered, the internal impedance will stop
most chargers doing anything silly. Excepting a very powerful garage type
one.

Even an old fashioned transformer, rectifier - raw DC of stated 4amp
output is more than capable of wrecking a perfectly good battery, if
left on charge. I know, I have done it.

Of course - if left on after the battery is fully charged. But that wasn't
the question.

--
*All men are idiots, and I married their King.

Dave Plowman London SW
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In article ,
Harry Bloomfield wrote:
charles explained on 08/02/2018 :
The main source of current drain is probably the radio. When you
switch it off, you're only turning off the amplifier, the tuning bits,
etc, are still powered. Alarms also take a bit of power.

Wrong - only the memories and clock are maintained with power off, a
matter of uA or a mA or so. My own car which is packed with maintained
electronics, satnav, TV and radio plus an alarm system, only draws 20ma
when in sleep mode after 1 minute.

Have you asked the maker how long you can leave the car and guaranteed it
will start - assuming a good condition fully charged battery?

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*HOW IS IT POSSIBLE TO HAVE A CIVIL WAR?

Dave Plowman London SW
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