On Sun, 11 Oct 2009 18:12:35 +0100, Dave Plowman (News) wrote:

How much use does a car need to keep its battery charged?

IIRC, BMW won't entertain a claim for a new battery if the car's not
been run for over three weeks. I've read somewhere.

So I start it, let it idle for 30s switch off, every 20 days? It's
been "run". B-)

To keep things happy, engine gearbox etc included, I'd say a car
needs to be driven so that it is fully hot for 10 mins or so about
once every two to three weeks.

--
Cheers
Dave.

on 11/10/2009, stan supposed :
Another yard stick read somewhere was; after some 12 to 24 hours after
being fully charged (not over-charged) a battery in good condition
should settle down and assume a nominal voltage of around 11.8 to 12
volts.

I agree pretty much with the rest, but not with the above.

A good 12v battery should still be above 12.5v after standing for that
period. Less than that and it has problems.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Sun, 11 Oct 2009 17:01:57 +0100, Fredxx wrote:

Agreed, modern cars have a "deep sleep" mode that they can be put
into.

I've not heard of this. But not saying it doesn't happen.

Reference is made to it in my Discos user manual. Not sure if it
gives details on how to put it to sleep or just on how to wake it up.

One issue when fitted to a car is that some of the car's gadgets do
consume a small current.

More than enough to flatten a battery in a month or so.

I had believed that batteries were generally shipped dry, with the
electrodes in their formed state, where on importation or before sale,
were topped up with the correct strength of sulphuric acid.

That would make sense for loose batteries. You don't want loads of
H2SO4 sloshing about in case of a leak or accident. Not quite the
same when fitted into a car though. And it would be a right PITA to
have to keep swapping batteries, or just fitting one and removing it
afterwards, each time you wanted to move the car. Much simpler to
have a "deep sleep" mode for the electronics.

--
Cheers
Dave.

Harry Bloomfield wrote:
on 11/10/2009, stan supposed :
Another yard stick read somewhere was; after some 12 to 24 hours
after being fully charged (not over-charged) a battery in good
condition should settle down and assume a nominal voltage of around
11.8 to 12 volts.

I agree pretty much with the rest, but not with the above.

A good 12v battery should still be above 12.5v after standing for that
period. Less than that and it has problems.

A lead-acid battery terminal voltage soon drops to 12V on discharge. It
really depends on the "period" you mention and the self discharge rate.

On Fri, 9 Oct 2009 18:08:09 +0100 someone who may be "Fredxx"
wrote this:-

You mix "trickle charging" with "charging voltage" in the same paragraph,

An assertion which is not correct as far as I can see from a quick
skim, but it is not worth any more than a quick skim. However, even
if I have done so there is nothing wrong with that if done properly.
Paragraphs are not limited to one concept, at least in writing
intended for people who can read more than a newspaper.

which suggests that your success in charging lead acid batteries has perhaps
been more by accident rather than through knowledge.

Which suggests that more work on comprehension of English is
necessary.

By the way, your other assertions indicate a certain level of
knowledge, but one which repeats some commonly held "truths" which
were overtaken by better knowledge some time ago.

I'll keep charging the lead acid batteries concerned (which are a
little different to the car batteries which the OP mentioned after
my posting) in the way I have been. They are coming up to their
estimated lifespan soon. When they do start to be less effective I
will charge their replacements in the same way.

You will probably want the last word.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Dave Plowman (News)"
saying something like:

According to an expert on another group the average lead acid car
battery loses 60% of its charge per month. I'm only quoting this FWIW
as it's not my experience. I have a clever electronic battery tester
which works out the actual capacity and that shows nearer 20% per
month.

Sounds far too high to me, unless it includes the quiescent drain.

Me too. But he came out with all sorts of lab tests to prove it. Makes no
difference - I've been using them long enough to know he's wrong.

Ah, a self-proclaimed 'expert' whose knowledge is derived from sales
brochures, perhaps?
Hmmm... now who does that remind me of?

On 9 Oct, 15:05, "Fredxx" wrote:

The best [Lead acid] charger has always been a constant voltage charger. *

Agreed, except that the voltage should change, as the battery
accumulates charge. A higher voltage is reasonable into a flat
battery, reducing gradually to the appropriate float charge voltage.
Starting out at the float charge voltage wouldn't get your battery
charged in any sensible timescale.

Note #2 is that this ideal voltage is slightly temperature-sensitive

Note #3 (important) is that float voltage is less than trickle
voltage. Constant trickle use kills batteries, just more slowly.

On 9 Oct, 13:40, (D.M.
Procida) wrote:
The charger says it's running at about 3 amps.

That means that the charge voltage is sufficiently higher than the
terminal voltage to push 3A into the battery

When can I consider the
battery properly charged?

Can't tell. Is the battery flat? Is the charger high?

On anything less than a submarine, 3A is a reasonable charge current
but a bad float current. So either your battery isn't charged yet,
it's dead and never going to charge, or the charger is over-
enthusiastic and is killing your battery as we speak. Without knowing
either the voltage, the design of the charger, or the specific gravity
of the battery electrolyte, it's impossible to tell.

With experience, you might learn that charge current for that charger
does indeed drop into a charged battery - but we can't know that yet.
If it normally does, then your battery is dead. If it never does, then
your battery _will_ be dead soon, once the charger has finished
killing it.

On the whole, batteries are expensive, Lidl's nice voltage-controlled
auto-charger is £13. Your call.

On 9 Oct, 17:16, David Hansen wrote:

I have been charging a set of sealed lead acid batteries in that way
for the best part of a decade. So far they remain fine.

Then you've been float charging, not trickle charging. The difference
is fractions of a Volt.

On 9 Oct, 22:59, "Fredxx" wrote:

I have known good lead-acid batteries keep their charge for nearly a year,
but it's rare.

I've an 8-year old, almost-unused, car battery in the garage (not on a
cold floor). It's checked regularly (hydrometer eye in the top) and re-
charged about twice a year. It still has sufficient power to jump-
start anything that needs it. Funny how long they can last, if not
abused. It _is_ worth looking after them.

In article ,
"Dave Plowman (News)" writes:

Incidentally, Lidl have their rather fine chargers on sale again from next
Monday. They can be left on indefinitely since they switch to a
maintenance charge when the battery is 'full'. They've gone up since last
time - now 15 quid - but still very worth it. Enough output to charge most
batteries overnight.

I saw a few in Aldi at lunch time, 12.99.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article ,
Andrew Gabriel wrote:
Incidentally, Lidl have their rather fine chargers on sale again from
next Monday. They can be left on indefinitely since they switch to a
maintenance charge when the battery is 'full'. They've gone up since
last time - now 15 quid - but still very worth it. Enough output to
charge most batteries overnight.

I saw a few in Aldi at lunch time, 12.99.

That's actually what Lidl sold them at. Must have been a mistake on their
website. Different colour from the old ones, though. Now grey.

--
*Time is what keeps everything from happening at once.

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