Battery warning on 2002 E-class

[tRoN]

So I am looking after a relatives 2002 E-class at their holiday apartment.
They use it when they come for a break maybe every 3 months for a week.

To keep the battery charged, I usually drive it around once a week, then its parked.
A new battery was purchased in November.

Recently, when we were away, the battery ran flat, so we jump started and she is fine.

However, ever since then, the display has a red battery warning that stays on constantly.

I went to the battery dealer who tested the battery & says its fine.

Any idea why this warning is still on??

 

[syrrano]

The red battery warning light indicates a problem with the alternator

If the light remains brightly lit with the engine running then the regulator could be faulty and the battery will run down again quite quickly
Another possible cause is that the brushes are worn down and not making contact anymore but this is often preceded by intermittent flashing of the red battery light as the brushes make and break contact
If the light glows slightly and becomes brighter the higher you rev the engine then the rectifier is damaged. The alternator will still be charging but not enough and the battery will run down gradually

Time to get to an auto electrician either way

A better way to maintain the battery condition is with a smart trickle charger which can be left connected and will keep the battery topped up while the car is in storage

 

[Colin62]

Yeah, what he said.

Don't take it to a Merc dealer - they will want to replace the alternator, and will want to charge you a fortune for it. An autoelectrician is the way to go, or a Bosch outlet.

 

[genetic]

The red battery warning light indicates a problem with the alternator

If the light remains brightly lit with the engine running then the regulator could be faulty and the battery will run down again quite quickly
Another possible cause is that the brushes are worn down and not making contact anymore but this is often preceded by intermittent flashing of the red battery light as the brushes make and break contact
If the light glows slightly and becomes brighter the higher you rev the engine then the rectifier is damaged. The alternator will still be charging but not enough and the battery will run down gradually

Time to get to an auto electrician either way

A better way to maintain the battery condition is with a smart trickle charger which can be left connected and will keep the battery topped up while the car is in storage

The battery light on the 2002 E class is controlled by a computerised battery control unit - it isn't directly wired to the alternator or regulator, so I don't think the possible diagnostic methods you posted will work with this car.

 

[Mars]

So I am looking after a relatives 2002 E-class at their holiday apartment.
They use it when they come for a break maybe every 3 months for a week.

To keep the battery charged, I usually drive it around once a week, then its parked.
A new battery was purchased in November.

Recently, when we were away, the battery ran flat, so we jump started and she is fine.

However, ever since then, the display has a red battery warning that stays on constantly.

I went to the battery dealer who tested the battery & says its fine.

Any idea why this warning is still on??

Jump starting the car and driving for a bit is not enough to charge the battery. Its still flat. You need to charge the battery overnight and see what happens after that.

Edit: You actually should get a maintenance charger if the vehicle stands alot. The Ctek chagers come with adapters that connect to the vehicle's terminals and stay there, then you just plug the charger into that when the car is not in use.
It is also one of the few chargers that is safe to use on the battery while the connected to the car.

 

[Mars]

This is the best one to use for maintenance charging:

http://www.ctek.com/en/chargers/XS 0.8

this is the connecter you connect to the terminals permanently and then just plug the charger into when you are not going to drive the vehicle.

 

[The_Unbeliever]

A trickle charger does that - it'll deliver just enough charge to keep the battery topped up.

A smart charger does the same, except that it'll discharge the battery with a tiny amount, then top it up again.

But your best bet is to get that alternator examined.

 

[tRoN]

Thanks for all the advice guys....saved me the hassle.

So off to the autoelec I go and later will consider the trickle chargers.