SI Batteries dead after replacing 2 months ago?

[JimJimFTWwin]

Hi guys. I had the usual fault on the cluster of dead SI batteries, so i replaced them and the rev counter worked a treat. Si lights didnt ever illuminate on this board so i didnt worry about it as i track all that myself anyway.

Car was stood up at the time with no battery being left on apart from when i was moving it to work on. Went to it one day and the rev counter was dead again so assumed i had damaged something in the process of sorting everything else out.

Had the dials out again today to check something and tested the batteries again, only for them both to register at 0.6v each.

Before i just replace them again, is there anything that can drain them like that fault wise?

[Speedtouch]

Ni-Cd (or most other rechargeable) batteries don't like to be left discharged for long.

You could try recharging and discharging them several times, which may bring them back to life...

[JimJimFTWwin]

Sorry, meant to say they were lithium ones!

Ive been using the car for the last week, and is now my daily so was hoping that might happen, but just wanted to check, and naff all so far. Was hoping if that was gonna happen, they would already be showing more than 0.6v.

[Brianmoooore]

Lithium batteries should power the board in standby on their own for a few years.
Check fuse 21 is good.
Not a good idea to disconnect the main battery when not using the car. Some of the electronics is designed to be powered continuously.

[JimJimFTWwin]

The battery the car came fitted with was dead, so i charged it up, but it died again as i wasnt using the car so i just left it off. I fitted a brand new battery last Saturday, and have been using the car daily since Sunday.

I've now been out and checked the fuse 21, and it checked out ok. Continuity was 0, and it also reset my OBC settings completely (13 button if it matters)

[Brianmoooore]

Are you sure you used the correct type of Lithium batteries - there's more than one?
They should be 3 volt Lithium, non rechargeable.
Are you sure the originals were Lithium?

[JimJimFTWwin]

Yes, definitely Lithiums removed, and non-rechargeable lithiums fitted. They were full voltage when fitted as I voltage checked them before fitting. They also worked great when fitted.

The batteries I used were Varta 1/2 AA 3v Lithium.

I have a spare set of clocks with another SI board in with the original lithiums still fitted (of course also dead) which i could re-fit with new batteries if needs be.

Only thing that does make me wonder is one board (the one i currently have fitted) has a small pin jumper on it (which is in the correct position for use) where-as my spare doesnt. guessing it makes sod all difference, but thought id check just in case.

[Brianmoooore]

The board with the jumper pin was supplied as a replacement at some time. The jumper disconnects the batteries when in the off position, so that they can be stored without the battery running down.
Boards fitted at the factory have a small wire link fitted near where the holes for the jumper pins are, presumably because BMW reckoned that the batteries wouldn't be significantly run down before these boards would be fitted in finished cars.
No current at all should be drawn from the batteries when they are fitted to a working car, so maybe your board has a fault with the power supply to the instruments, and the batteries are powering the whole board when it's in use.

[JimJimFTWwin]

ahh ok. well ill try replacing the batteries on the other board and try that one. I appreciate all the info, so thanks!