Auto Stop/Start warning light

[Sgt Joe Roberts]

Looking for some help with the Mrs Countryman Cooper S. We spent three months away in Portugal Jan-Mar so I disconnected the battery on her Mini. Since reconnecting the battery the Auto Stop/Start warning light appeared. The battery is fully charged and when I turn the Stop/Start off the warning light disappears but it does come on as soon as the car is started. Any ideas what's causing this and how to fix it? Thanks.

[E-bmw]

Firstly, what is your gauge when you say "fully charged"?

Secondly, do they just have 1 battery or is there a separate start battery as there is in many stop/start cars?

[Sgt Joe Roberts]

Just the one battery and I've put my battery charger on it and it's telling me it's fully charged. A bit more googling has suggested it's a sensor issue. I hate this bloody car, she likes it so I guess it's going to be with us for another while.

[BOR]

Fully charged doesn't necessarily mean the battery is OK, Sarge.

How old is it?

With time, the battery capacity reduces, and once it starts approaching 80% capacity, Stop/Start will be disabled.

It could be worth buying a replacement battery and fitting it yourself, even if it just rules out the battery as being the problem.

It's time consuming to remove all the plastic, and it should really be coded as a new battery to avoid any issues with the charging system, but straight-forward to do.

[E-bmw]

As a minimum starting point you need an accurate check of the voltage on the battery when at standstill.

A good fully charged battery is around 12.6 or 7v, anything less than that is around 10/15% capacity lost for every 0.1 volts, so if all you have is 12.4v stop/start won't work.