Originally Posted by cvbdsl
I believe the BIRD is supposed to prevent this?
I don't believe so. I'm not an expert, but my understanding is the the BIRD just controls when the coach and chassis batteries are connected together to allow one charger to keep both sets charged. It does not serve any function to limit overcharging.
Any control over overcharging comes from the charger itself. I'm having trouble finding a manual or specs on your unit, but it seems like it's a three stage charger? If it's working properly, it should keep the batteries charged and not over charge them. I asked what kind you had, because if it was a simple converter it could easily boil the batteries dry over the winter.
From the looks of your batteries, and the way the sides are pushed out, I would guess the battery froze. I hear the plates can swell and short out when boiled dry, but I don't know if that causes enough expansion to crack the case open like that.
Whatever the mechanism for battery failure, I would suspect that something is up with your inverter. Either it has failed and did not charge the battery over the winter (the more likely scenario) or the control circuitry has filed and it was over charging it. Either way, I would thoroughly check out the charging function before spending money on new batteries.