[:@] I have a new alternator and battery after the car wouldnt start and I needed a new alternator...I decided to get a battery as well..A couple of months later, it's DOING IT AGAIN..the battery light is on very dim but lit as well as the other warning lights when the car is on. It sometimes doesnt want to start at first but does, other times it starts right up! But those lights stay on and when i AM DRIVING THE RADIO WILL CUT OUT AND THE A/C AS WELL then...turn right back on??? Is something going bad under there, or could the aftermarket alarm or my amp be doing this? I also noticed that even when I turn the a/c off the compressor stays on..this could be b/c I had a vacuum hose problem and not getting any air whatsoever out of the center vent so I reached down in there and snapped the flap off so air could blow out until I come up with the 1200 to fix that little problem. Any ideas as to why Im losing power???Thank You. ~Dehaven.

 

check your ground cables. especially from battery to body, chassis to engine. clean those terminals.
check for battery drain. you should not more than 0.4 amperes when the car goes to sleep mode.

 

Also, I would check your drivebelt tension to make sure the alternator is pushing out those amps, and the battery isnt having to make up for it intermittently. If your belt is loose, this could be the case.

 

I know you posted this back in 2004, but maybe you still visit this forum. I have an 86 300E with the exact same battery draining problem you describe. Did you ever find out what was causing it? Any info would be appreciated.

 

Hi Dude, I had a similar problem with my 87 300D Turbo. After a new alternator, a new battery, the battery still died. Turned out that the belt idler tension spring was broken, which had caused the alternator not to come up to speed and keep the battery charged.

 

I have a 1995 s500 that keeps draining. The alternator is new and the battery is new. but it keep draining to 335 cca help!!!

 

Check the alternator output voltage. 13.5 volts is minimum. If alternator voltage is low, check accessory belt for slippage. On my '87 300 the accessory belt tensioning spring was broken, causing the same symptoms you describe.

 

alternater to battery fault, replace temp control unit with a salvaged one

 

i replaced my stock 60 amp with a 90 amp 5 years ago and all the same symptoms went away. yellow driving lights are a real drainer. low voltage causes resistance and heat in all circuits.

 

90 amp alternator that is, try a more powerful alternator