BMW 318I 1986 SI Board Battery Problem

[Shep123]

I have had the battery off on the BMW to charge it as I only use the car now and then. When I put it back on I noticed the Rev counter and Economy gauge was not working. I have read that this is due to the batteries either need changing or they are flat on the SI board.

Can any one tell me if they will recharge themselves now that the main car battery has been charged,

Many Thanks in anticipation of any help.

[Jedz123]

From what I've read on this forum if you let the car sit over night with a fresh battery and if your SI board batteries are still able to be charged that they will be charged in the morning(your Gauges will work). If not your batteries are dead.
I just replaced mine for my Tach, Fuel econo. and Temp gauges were not working. I took out the old batteries and there was allot of corrosion on the SI board for they leaked like a sieve. I replaced them with Radio Shack NiMH batteries but only the temp gauge flickered back to life after the replacement. My Tach and Fuel econo. will jump erratically periodically but I think the SI board was to far gone for there to be any hope for them to come back to functional life. I plan on getting a new tach anyways for I have a new performance chip coming in next week and a 325i cam with springs to follow shortly after so the old 5k tach would be useless.