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.

Cheers, T i m