I have a 2005 SRT-6 - one of the "new" old SRTs - bought 8 mos ago with 98 miles on odometer. The last couple weeks I noticed the car started turning over slower and slower until the battery went dead. I don't drive it much - 3K miles on the last 8mos. I have a battery charger, charged the battery and car is fine again - except as time goes on, car turns over slower and slower until dead battery. Checked the battery and it is sufficiently hydrated. Any thoughts? I am thinking alternator or other charging issue. I noticed some on the forum have had "Relay Control Module" replaced and there was some talk about a Mercedes recall for battery and alternator issues. I have double and triple checked all lights - hatch area, glove box and switched off the dome lights etc...nothing is on and I have not done anything or installed anything differently than the first 6 mos of ownership.

 

did you check the strength of the electrolyte? I'm sure the battery cells are good, but if you don't drive it everyday theelectrolyte will get weak., you can buy fresh acid from pepboys if required, if a cell is getting worn I would replace with a deep cycle marine battery, since you let the car sit a lot.

 

Could also be some module malfunctioning staying on. Called parasitic draw. Even though the car is off, a lot of systems (modules) can still be on. Biggest one would be your Body Control Module. Easiest way of finding how much current is being drawn is with multimeter in between + cable and + post. Remember, checking current is done in series unlike voltage which is parallel.
Another thing, batteries and alternators almost go hand in hand, as the battery weakens, the alternator is stressed harder and harder to charge the battery and a weak battery can cause alternator failure.

 

Yea, I've read on the MB forums that some owners have had problems with their heated seats drawing current while the vehicle is off. You might want to check those out? I would be tempted to just unplug them and see if that cures your problem.

Here is a thread.

 

Do a search on here for dead battery. There is a small module that (if I remember right) costs $77 and when it dies it drains your battery. I believe this has been the woh's of a couple member's dead battery problems.

 

Thanks - I am going to check the "strength of the electrolyte" and do an ingition off draw test. According to the Service manual it should not exceed .035 amperes and hopefully one of these tests will point me in the right direction. I am guessing battery problem only because it's a 3-4 year old car that sat its first 3 years of life. I also found something called "Acid stratification- A common cause of battery failure is acid stratification. The electrolyte on a stratified battery concentrates on the bottom, causing the upper half of the cell to be acid poor. This effect is similar to a cup of coffee in which the sugar collects on the bottom when the waitress forgets to bring the stirring spoon. Batteries tend to stratify if kept at low charge (below 80%) and never have the opportunity to receive a full charge. Short distance driving while running windshield wiper and electric heaters contributes to this. Acid stratification reduces the overall performance of the battery." Sounds like something that could have happened to a 3-4 year old car too.

 

Just FYI to close the loop on this problem (hopefully). I did the ingition off draw test and my car was hardly drawing anything from the battery - hence eliminating a draw on the battery. I did a spefic gravity test on electrolyte and even after a 10 hour trickle battery charge it was showing poor-fair charge - so I am guessing a bad battery (it was almost 4 years old). Bought a new battery at Autozone (84 mos - $109.99 - Chrysler wanted $147.99 for an OEM 72 month battery) and all appears well...of course won't know for sure for a few days/weeks. Thanks for all the input (Maxwell, Jeep2Xfire, msheredy &dyezak - I'd buy you all a beer if I could).