time2roll wrote:
You probably killed it. You can do that to any battery.
...
Otherwise the WM battery is fine.
x2.
Using battery only while on the road, for stand-by emerg break only, any 12V battery will do. He either killed it or it was a lemon. The question about "best battery" is of little importance in this scenario. Reading/learning about battery maintenance will be more productive use of time and money.
I would also think that under- or over-charging a battery due to poor converter would take much longer than 15 months of intermittent use to kill the battery - and to notice this - when battery isn't really used, sitting in standby. But I could be wrong here.