Jan T

Is there a proper way of testing the trunk battery? I tested it with a meter daily to see how much it drops without driving the car, and started with 12.60, then was 12.31 three days later. So to me that doesn't seem bad. But then I was thinking if I had a weak trunk battery not holding charge well, whether it may be sucking charge from the main battery while it is sitting there and therefore not loosing charge that bad? I usually use a trickle charger, but notice that if I leave the car without it for a couple days that I get the consumers off line notice which goes away after running for a few minutes. So I figure I need a new battery, but was more questioning if my meter testing mentioned above is flawed due to having the two batteries in the car. Discharging to 12.31 after 3 days just didn't seem that bad to me.

Plus today, I drove it, parked it and tested it and within a 2 minute timeframe with the meter on the car I watched the meter go from 12.45 up to 12.60. That made me think it may be drawing from the main battery. Why else would the meter raise like that?

pjdough

Got the same prob myself. I went ahead and replaced trunk battery but within days was getting the "convenience accessories not avail" warning for several minutes after starting my car. My indy investigated but found no noticeable draw.
I keep the trickle on, but would like to know what the draw is.

MJ50

how old is the battery?

Jan T

Maybe the proper way to test wether it is holding charge is by disconnecting the negative post in the rear battery, take a test meter reading, and let it sit 3 or 4 days and test it again to compare. I suppose that way it would be independent from drawing from the front battery. I don't know, just theorizing.

Viper98912

I thought someone had posted on here that when the car is off the batteries are not connected. They're only connected when the car is on to charge the rear battery. Or so I thought....

Jan T

It's nice having 2 similar cars to do testing. After 4 days of constant trickle charger on my SL65 and SL600 rear battery to create a baseline, I tested both at the battery, and SL65 had 12.60 and SL600 had 12.93 reading. Then wanted to compare over night if the SL600 was loosing charge too quickly, so I took the charger off both cars and tested again in the morning. Found that the SL600 was 12.39 and the SL65 was 12.24. I thought that was odd because I get the consumers off line when I start the SL600 after an overnight sit but not with the SL65. What the hey....

F1BHP

It could be the starter battery as the aux battery is used as a backup for the starter when it gets low and has a relay that gets activated to give priority to the engine start support which would cause the consumers off line alert even with a healthy aux battery.

Jan T

Interesting thought on the starter battery. I will let both cars sit for 3 days and then test meter the starter batteries on both cars.

Jan T

Well, I let the SL600 sit for 3 days and took a reading, and the front was 12.61 and the rear was 12.40. To me I thought those readings seemed ok being above 12, but maybe I am wrong. I found this chart on the internet with ratings.

Ingenere

I have had my SL55 since '03....... The problem is buy a new battery!

Jan T

I agree, the day is approaching to try a new battery. That will probably fix it. But just odd that it seems to read good on the meter, and my SL65 reads lower than my SL600, but no consumers off line on the SL65. But I understand more goes into testing a battery than just standing test. I may stop by autozone and see if they can do a quick load test on it.

coldhammer

i bought a new rear battery last year because i was told it was shot.

even with a brand new battery fully charged after sitting for 4 days i get the accessories offline error. Yet i know others that can go for about two weeks before they see the issue.

As of yet i can not explain the difference in timeframe.

Jan T

Went to autozone and they tested the battery and teat said it was bad. Went to Fletcher Jones and got a new one, 270 or so with tax. Probably should have saved $ elsewhere, but what the heck. Then discovered vent tube holes on the battery, but old battery didn't have any tube, so the new one didn't have any either. Maybe need to pay extra 50 for that, or use a straw from McDonalds. I wonder how critical that tube is anyway, as it is not like the entire trunk is sealed completely, for instance vent hole is still in the trunk floor.