Quick question, I have a 2017 Thor Miramar and I have replaced my chassis battery back in December '18 and now that battery has gone dead too but is still rechargeable. I'm 99% sure the BIM is bad. So my question to the group is, what can drain a battery besides an alternator and BIM? Also, this fall when I went to put it in storage I had to jump the battery and drove it for 15-20 minutes to my storage area and week later I was able to start it without jumping/charging it. This leads me to believe the BIM is bad. Any thoughts? Thanks in advance!
Alternators charge batteries.
BIMS connect two batteries (or battery banks) together when one side is charging and separate them when neither side is charging.
A BIM with an internal short MAY discharge a battery.
An Alternator with an internal short MAY discharge a battery.
Anything connected to the DC buss will discharge a battery if energized.
Anything connected to a DC buss MAY discharge a battery if faulty.
Put an ammeter on your chassis battery with everything turned off. The only draw would be in milliamps for maybe the memory in the radio. If you have more than that lift the lead on one suspected component at a time to see if the draw stops. If your case the BIM and or the alternator. If neither one of them are the culprit then it's a major guessing match. I'd move on to the major fuses and relays in the fuse box next.