I have a 2008 is250. My previous 3 batteries only lasted 2 years max. I got a new alternator few years ago and didnt help. My last battery lasted 6 months. I got a new battery last week at Sam's club and it died after only 1 week. According to the mechanic, I have a failing negative ground cable. I checked all over internet and couldnt find anything new. Found a bunch of preowned cables that would have taken forever to ship and I need my car asap. After calling 3 local dealers found the cheapest for $102. Will pick up today and well see if that was the culprit.

 

There are some sime tests to be done that could support this... Obviously we can't see inside the cable but tell tale signs are lumps, corrosion, cable heating or smoking when cranking or under high load (drain or charge).

Do you own a volt meter?

 

Replaced ground cable and it looked corroded. When cranking the car its much smoother. Seems for sure problem fixed.

 

Test with a multimeter for continuity and resistance