Micra battery at... 1 volt!

Absolutely. But it wasn't really ina low state of charge. If he'd stuck a hydrometer in he'd have found that it was still nearly fully charged, but the electrolyte just couldn't get to the plates to do its stuff.

Ian

Maybe I didn't mean sulphation. Coats the plates, at any rate.

Yup. Without a doubt.

An extra 500mA does seem to be about the magic figure. Car batteries, you see, are not designed for low discharge rates. They are designed to give a hell of a discharge rate for starting, to recharge from the alternator and then to do more or less nothing for 99.9% of their lives, as the alternator supplies all running needs for the car.

Try it. Leave a drain on overnight, deliberately. Something in the range 0.5 - 1A. Then see how happy your car is to start in the morning after losing something like 5% of its nominal capacity.

Ian

Tried that fairly often, it's fine. What's your point?

Not a problem with either of mine.

Many modern upmarket cars will discharge their battery over about 3 weeks to the point where it probably won't start.

So a couple of days of non use will give you that figure.

It does seem to be related to the rate of discharge. If it's small enough not to have the no-starting effect for three weeks then of course you wouldn't expect much to happen in two days.

Ian