I just bought whatever battery Amazon says fit. I wish I bought the APC name brand, but whatever. The good news is it came in the mail and after some testing it seems to be working. Came drained it seems and was giving an error, but I let it charge for a while and the errors stopped. Still charging now, but seems to be working. I will test under load maybe tomorrow before setting up fully and running wiring. I think that was my mistake the last time I just plopped everything together and didn't really test it all. The old battery is still under warranty and seems like I should be able to return to manufacturer for refund, but says to return in original box and I don't have that. I'm curious if they let me mail a leaking battery anyways. We will see. I will start an RMA and see what happens.
Still may just buy one of those tripp lite isobars like TBB mentioned. Seems like a good piece of equipment.