Wow! First of all, Welcome to the FRF. Now lets see if we can interpret what your issue(s) is.
Here is what I understand you said: Your unspecified Forest River product has 3 slide outs. You were having problems with them so you replaced the battery. “It” kept tripping breakers. Hmmm Both your slides and battery are 12v so I’m going to assume you meant blowing fuses rather than tripping breakers. So you replaced the fuses and the slides functioned normally. So now I gather that the slides were never the problem. It was, and is, the power source. Now your battery is depleted and you are plugged into shore power. That tell me that your charger is not working. Now there is also no 12V system power. That tells me your converter is not working.
First thing I suggest is to get your new dead battery on a charger and try to save it.
After that, check to see that your 120v appliances are working. If so, I suggest that you focus on your converter. Since you stated that it is a new battey, check the reverse polarity fuses on your converter. If you have a deck mounted converter, they are on the back where the battery cables connect. If you have a built in, they are in the front of your power center.
Please keep us advised.
Welcome to Lake Wobegon where Justin and David utilize abductive reasoning to help solve F/SS issues.
Happy Trails and Remember the Pequod.