Today I checked my aux battery for the first time. I've owned my E320 for two years and am the second owner. It has 59,8xx miles on it. The aux battery took 1.5 cups of distilled H2O to bring all six cells to the proper level. To date I haven't had any messages alerting me of any electrical concerns. Should I hook my deep cell charger up to the battery or let the alternator do it's job?
The main battery in the trunk appears to be sealed with a label stating: VRLA Battery Do Not Open. There are six caps on it but a screw driver or knife will not open them. Their design is unusual for a screw type cap. All labels on it indicate that it was made in Germany. If the aux battery was low on H2O I'm positive that this one could use some also. Any ideas/comments?? Thanks...

tarheel76

 

2004? If these are the original batteries, then they're 7 (possibly 8) years old. That's about the lifespan, so they don't owe you anything.

If it was me, I'd replace both of them. But it's your choice.

 

I agree. Based on what you found If it were mine I would replace it.

 

Both appear to be original equipment and I will replace both at the same time.I have found a source for the main battery but haven't checked a source for the aux. In the mean time since I just added H2O, CAN I/ SHOULD I put a charger on the aux battery while it is still hooked up and will it affect the main battery in the trunk? Being a senior and retired I have to plan for expenses such as these in advance and have a plan in place when the time comes. If it's not broken don't fix it. Last but not least this may seem like a DUMB question. What is the purpose of the aux battery??? Thanks....

tarheel76

 

tarheel,

My '03 E320 has AGM technology for both batteries, so I don't know why you're putting water in the aux.

I've replaced both in the past -- main battery was from Napa (Deka) and the aux I bought from the dealer -- there are posts here where people have identified AGM motorcycle batteries for the aux replacement with same size/properties. Replace AGM batteries with other AGM technology -- don't put a wet acid (aka "flooded") battery in there as the charging rates are different and the wet acid battery will cook and eventually fail.

BTW, when you're playing around with disconnecting batteries, make sure things that are set on automatic (i.e., headlights, wipers, etc) are turned off before battery work.

Regards,
paul...

 

The Aux battery should be a sealed AGM battery. You should not have been able to add water to the battery. I replaced my aux battery with a Bike Master Tru Gel battery purchased on ebay. It came sealed and charged. All the AGM batteries that I found in stores needed the acid added and an intial charge. I didn't want to mess with the acid.
My battery was the original with 90,000 miles and 7 years on it.