I have a 2003 Sebring I bought used. It ran fine with no problems. I don't drive everyday, maybe only every 5 to 12 days, but after several months, I noticed the battery losing power. I bought a portable jumper and it always started using that. Driving the car charged the battery. There were no Check Engine, Battery or Alternator lights on, and it only has 183,000 miles.

Over the next several months, the battery started draining at a faster rate. Instead of lasting 7-10 days, it would only last 5-7 days, then 3-5 days, then I was having to start it every day and let it run for 5-10 minutes.

Eventually, I had a Chrysler dealer replace the battery. That was December 2017.

The batter lasted about 9 months before it was back to its same old tricks, and now I'm back to the same thing, having to use the portable jumper and driving it around to charge it up.

If it is the electrical system, shouldn't I be having this problem all the time?

I don't understand why the battery worked so well for 9 months before problems started cropping up again.

Any suggestions are appreciated.

 

Check for excessive current draw. With everything turned off, doors closed, key off, the current should be less than 0.050 amperes (50 milliamps). That's the current required to run the clock and the receiver for the keyless remote. If it's more than that, look for the reason. Make sure that there are no lights on in the trunk or glove box or anything else. You say that the car sits undriven for days at a time. When you do drive it, are you driving it enough to charge the battery fully? It could take more than a half hour of driving to get the battery charged back up. If you are making short trips it may not be enough to get the battery charged. The constant low drain may be pulling the battery down slowly and short trips are not bringing it back so that the net result is a slow process of flattening the battery.
One solution could be to pull the IOD fuse. In the fusebox at the left end of the dash, you will find a fuse with "ears" on it in the center of the panel. Pull it out slowly, just far enough to disconnect it. That will kill power to the clock, power seats, interior lights, and keyless remote unlocking. Those are things that are either always on or always available even without the key. It will prevent draining the battery while the car sits unused.