battery eating M3

[committed]

My 1998 M3 Evo has got through a battery a year for the last 3 years. I end up needing a daily jump start following the cold of winter.

Once started the battery takes a good charge form the engine but it doen't hold it for more than 12 hours, then I end up buying another battery.

If it was a drain then surely a new battery would suffer the same fate but it doesn't start happening until about 10 months have passed.

I've been told that if the battery isn't matched correctly to the car that it never receives a complete charge & will eventually fade to nothing, but surely I can't have been sold the wrong battery 3 times in a row? Has anyone had a similar experiance?

Can anybody help before I start the trip to an auto electrician.

[Huliganov]

Get it checked out. Go to a local garage and ask them to get one of those electronic box testers on it. If the charge is at a constant number (around 12.5v +) and doesn't decrease then it sounds like your alternator is failing to charge the battery. If the number does decrease however the battery needs changing.

Personally I think it is an alternator issue with your car. Get it checked out.

[Ayrton4ever]

could be the battery indeed, sometimes you buy it, you think new and it has been sitting at the warehouse u bought it from for years....although this to me sounds highly unlikely

I would have the alternator checked to see whether it actually charges the battery

[Huliganov]

What type of battery is it, a D096, D075 or a D065?

[committed]

Huliganov said:

What type of battery is it, a D096, D075 or a D065?

I'm pretty sure its a DO75. I know that if you fit a battery with the wrong amp hours that it will never reach its full charge potential and will degrade just as mine have.

As you say it could be an alternator fault or I could be being told that the wrong battery is the right one for my car. I've bought them all form Halfords.

Do you know which one it should be for a 98 Evo coupe SMG? Thinking about it I may never have stated the SMG which might have made the difference?

[Huliganov]

E36 and E46 M3's have a D096 battery, I'm fairly sure of that. The E30 M3 is less complicated, has less electrics and needs less power to run it so I think a D075 is just fine. You could even use a D067 too. Personally I think its just fine to run a higher capacity battery, you'll get less problems starting up in the morning on cold winter days, the car will start almost every time first time and everything has less propensity to shorting too.

You should get it checked out though, it does sound like an alternator problem because a D075 battery is more than adequate to run an E30 M3. However, if it is the battery change it to a D067 (higher output I believe) or even a D096. That should cure the gremlins but personally I believe you have an alternator problem.