Battery Problems

[bdelmonico]

I have a '92 500sl. The car is driven 1x a week, may be, for a short distance. The battery is going dead after about 30-45 days. I Replaced the battery w/ duralast 49-dl. Not only did the battery go dead it was rendered unchargeable. This happened 3 times in a 90 day period. I replaced the new battery with another new batter 3 times. Question: Can a battery drain cause the battery to be rendered unchargeable? Additional info. I live in a very HOT area of the country. In the last 90 days the temp in the garage has been 105-110 24 hrs a day. Any Ideas.

[tecqboy]

In my considerable experience I've found that indeed, even a new battery can be discharged so throughly that it cannot be re-activated. This is particularly true of the totally sealed type of battery. The alarm / remote door locking system is always active on this vehicle, so it's inevitable that the battery will go dead after a few weeks storage What you need to do is get a small 1 or 2 amp "battery tender / charger" to use while the car is in storage. That is of course if you have a place to plug it in for 110VAC power. There is also a device, sometimes called an anti-theft switch, which you can put on the battery to totally disconnect the battery from the car. But a beautiful car like your's should be driven and enjoyed often.

[bdelmonico]

Thanks. I did not realize that there are so many devices still active on the car while it is off. I knew about the clock and computer but that's about it. I thought i had a short or something. Ok, i will look into a battery tender. Will that cause any issues with the computer on the car or any other electrical items? Thanks again

[tecqboy]

I store my 1991 SL November through April with a 1 amp tender and I've never had any problems. I live in Wisconsin where it can get quite cold.

Another "issue" with the 129's is that the switch for the trunk lamp is known to break. The trunk light stays on after the trunk is closed. Just like a refrigerator, you don't see it. But it will drain the battery in 2 to 3 days time.

[Mike Miller]

I bought a great battery tender at Kregan Auto Parts. You hook it up permanently to your battery and mount the unit off a braket in the battery compartment. It has a little pigtail 115V AC plug that is easily hiden in the battery compartment. When you are going to store the car for a while, just plug it in like an electric care (ugh!). Seriously, it really works great on the wife's BMW.

As for my '92 500 SL, well I drive it every day and far and as often as I can get away with!!! No problem of battery drain on that baby.

[bdelmonico]

Originally Posted by tecqboy

I store my 1991 SL November through April with a 1 amp tender and I've never had any problems. I live in Wisconsin where it can get quite cold.

Another "issue" with the 129's is that the switch for the trunk lamp is known to break. The trunk light stays on after the trunk is closed. Just like a refrigerator, you don't see it. But it will drain the battery in 2 to 3 days time.

Ya, i heard about the trunk light issue. So I stuck my camara phone in the trunk and closed it and took video. there was no light on. Thanks. I am going to try and drive the car a little more. If the battery goes dead again i will look into a tender. With the duralast it is free replacement for 2 years. Those guys @ autozone are getting real sick of me. I will give it one more shot before i go with the tender. thanks again.

[rfpmoxie]

The Deltran Battery Tender Jr. that I bought at Pep Boys ($39 , I believe) is a great item. I've used it for 2 winters and heartily recommend it as my R129 is hardly used from Nov - March. Each time I start it and take it "around the block" during this period, it turns just like a new battery would. Although previously mentioned, when you lower the trunk lid ( it will not close due to the tender cable), make sure that you have turned off the light (switch right beside it)! Good luck, Ron

[caesarang]

I have that problem too. I drive mine once a week too. Have change the battery once in the last 12 months. Thought the battery was just dead. Had to jump start every other month,. Once I use to just leave the car idle and let it charge up on its own but it killed my alternator and cost me a bum. Now I just send it down to the garage to get it charge up when it goes flat. The charger sounds interesting but I do not have a powersource at my garage. I notice a plug from damon tweeks that they sell online that at a turn of a screw it disconnect the power supply. Easy installation. Thinking of getting it

[TX76513]

As mentioned above a battery tender is indeed the trick for less than $10 - if you do not have power purchase a solar battery charger/tender. These can be found for <$20 and work just as well. The panel can be mounted on the garage roof and the wire lengthened easily