Hi Guys,

A week ago I had an issue with my 280E (M104) which involved the battery going flat repeadidly. Each time I would recharge, and after a couple of days it would end up flat in the morning. One morning I jump started it but after a 20 Minute trip it hadnt taken any charge.

Battery voltage = 12.03 Volts
Voltage at battery poles when engine running = 14 Volts
Current draw at rest = 200 to 300 MA - Probably 400 MA with alarm on

Does this mean my alternator is charging sufficiently?

I replaced the battery on this occasion, and havent had any problems for a week now.

However the thing I have trouble with - is the battery is sitting in our project car (XJ6 Jag). After an initial charge is has been able to crank it and start it each day for a week without even sounding flat.

Can any one give a logical explanation for this?

__________________
1985 190E - Gone
1989 230E - Gone
1995 C200 - Gone
1993 280E 120000KM - Built like a brick, the best one yet

Current draw doesn't seem excessive. Voltage at battery with engine running is good.

The only type of battery that is designed to withstand repeated deep-discharge events is a "deep cycle" battery. Car batteries are not "deep cycle" batteries and repeated discharge events like you describe will eventually result in a battery that will refuse to accept a charge.

In your post you didn't indicate how old the battery was that was going flat all the time. If it was new, I'd suspect a defective battery, if not - maybe it had exceeded its time allotment here on earth.

If you've replace the battery with a new one and the problem hasn't returned - you've answered your own question.

That resting rate is 10 times 'normal'. Should be around 35Ma. Something is staying on.

This is somewhat embarassing. I retested and discovered I was looking at the wrong range on my test meter. IE not 300 MA rather 30......

Battery is still fine after a week, Im gonna put it down to the old battery being on its way out - but not completely fudd.

__________________
1985 190E - Gone
1989 230E - Gone
1995 C200 - Gone
1993 280E 120000KM - Built like a brick, the best one yet

Well here I am a month down the track. Started the old girl this morning. Sounded a little flat. I have a couple of questions:

Does a new battery require charging before use?
Is a CCA of 300 Sufficient for a m104; our climate never goes below 10C. The guy I talked to at the auto store recomended a 250CCA, I however decided to get a higher rating.

__________________
1985 190E - Gone
1989 230E - Gone
1995 C200 - Gone
1993 280E 120000KM - Built like a brick, the best one yet

A new battery should not need a charging upon purchase - in the US all batteries are stamped with a date code in the tops (melted into the plastic) so you can see when it was made - a month old is fine. Have the parts house show you the date stamp.

As for the CCA ratings, a 300CCA battery is not much of a battery. All the batteries I put in my cars range from 450CCA up to 800CCA for my diesels. 250 seems even more "weenie".

Hope that helps, you kiwi (I'm using the new terms I just learned!)!!!

__________________
- Brian


1989 500SEL Euro
1966 250SE Cabriolet
1958 BMW Isetta 600