On 24/10/2019 16:07, T i m wrote:
On Thu, 24 Oct 2019 13:59:04 +0100, "dennis@home"
wrote:

On 23/10/2019 18:07, T i m wrote:
On Wed, 23 Oct 2019 15:37:02 +0100, "dennis@home"
wrote:

On 23/10/2019 14:18, T i m wrote:
On Wed, 23 Oct 2019 13:32:48 +0100, "dennis@home"
wrote:

snip

5W for 24 hours would be 120 watt hours; at 12v = 10 AH - quite a drain on
a small battery,


What do you think the capacity is for a car battery under a very small
load like that?

Erm, roughly the rated value at that load, given it's normally the C20
one.

Rubbish.. a 40AHr batter C20 rate is 24W not 5W.

Possibly, when new and when at 20 DegC and down to 100% discharge.

One fifth the discharge rate will nearly double the capacity of a lead
acid battery.

Agreed, but see above (and depending on what capacity rate you are
referencing).

The point being is that it's quite easy to flatten the battery of an
old vehicle in the cold with just a boot / interior light, overnight.

A mate did exactly that with a Rover SDi and that wasn't that old.

No but the battery or charger were broken and needed fixing.

The battery may have been old but otherwise functional if used within
it's normal constraints (like not leaving an interior light on
overnight).

Its normal to be able to leave all the parking lights on overnight, not
just one interior lamp.

What are you going to do if you have to park on a road with other than a
30mph speed limit which requires parking lights?

I haven't said that it wouldn't drain a faulty battery.

It wasn't a faulty batter, it wasn't a battery at 100%, like many
batteries aren't. It was able to cope with it's *normal* day to day
duties, just not an extreme case, just like many 'not new' batteries
on many perfectly otherwise functional vehicles.

At what point off 100% capacity would you consider a battery to be
cr@p, 50, 75, 99%?

Well the stop start stops working at about 75% so that's faulty.

Do you think they last forever? They are consumable items like tyres.