Back in June, on my Summer road trip with my son, we logged over 1200 miles with no issues with my teardrop trailer, using my 150W suitcase solar panel to keep things charged up while camped for up to 5 days without moving. At home I typically check the status of the trailer battery a couple times a week, and it's been in a good range. I have my trailer plugged in inside my garage, but use a timer to limit the charging to 90 minutes, three times a week.
Yesterday I checked the status of the battery and it was down to something like 5-10%, which I never see. I turned on the timer and left it on for 24 hours. When I checked this afternoon, it was nearing 90% charged according to the battery monitor. I then unplugged the power cord to let things settle. I checked back 10 minutes later, and the voltage was dropping like a rock and was around 15%. The battery itself was quite warm, but that doesn't surprise me given that it was charging for 24 hours. I can't see that my onboard charger would be at fault given the symptoms, and I don't see what else could be going on other than battery issues. My fridge was not turned on or plugged in, all my lights were off, my radio was off, my Fantastic Fan was off, and my mattress warmer was not plugged in. I can't think of anything else electrical that could have been left on to drain the battery and damage it.
I have a Nasa Marine BM-1 Compact Battery Monitor installed in my teardrop to check the status of the battery and charging current. The BM-1 uses a shunt to measure the voltage change.
Time for a new battery? I currently have a Group 31 Sears Diehard Platinum AGM that's about 5.5 years old. Sears doesn't have this battery anymore so I would need to find something else.
I do see that Lifeline has a Group 31 Deep Cycle battery (GPL-31XT) that provides 125 AH. Best I'm finding is around $400. One concern I have is if there's a problem, there's not always a Lifeline dealer nearby. That's what I like about Sam's Club and Costco, and used to like about Sears. I do want an AGM deep cycle battery.
GPL-31XT - Lifeline Batteries
[EDIT: forgot to add that I have a 12V 15A Samlex charger, very similar to this current one]