Signs of a Bad battery?
A short history...
At the end of Summer 2011 I purchase my HTT, it came with a cheap-o Group 27. A couple weeks after the camper purchase I bought another cheap-o Group 27 and connected it, in parallel, with the original battery. They have always been wired in a set since I purchased the 2nd battery. I remove the neg connection whenever camper is in storage. In the winter I bring the set home, and every 3-6 weeks connect the set to my bulk (not a fancy 3-stage thingy) 10A charger for a few hours. The few times have have gone dry camping over the past 18 months, I connect my small Honda 700c genset to the camper for ~1 hour each day to keep the set topped off. 80% of our camping nights we have hook-ups.
Fast forward to this past week...
I purchases a Battery Tender to keep the set charged over the winter. I connected to the Tender to the set and after ~24 hours it was still in bulk charging mode, despite the fact that I had a couple of weeks earlier connected it to my cheap-o bulk charger.
At this point I separated the set and connected the Tender to original battery. 48+ hours later, the charger reached Stage II and less than 18 hours later the charger reached Stage III (final stage). The battery also "boiled over" a bit as well, but that might have been due to me adding water prior to the original charging (I have since read that you are not suppose to add water under the battery is charged).
I connected the Tender to the 2nd battery. In less than 18 hours it reached Stage III.
Should I be concerned that something is "wrong" or "gone bad" in the original battery?
TV: 2008 Ford Expy
Camper: 2012 Rockwood Roo 233S
12V: 2 x Group 27 plus Honda Ex 700c Genset