It’s unlikely your battery problem is from the interlock. So your wife isn’t paying. It’s just a battery that’s gone bad. Pain, but the usual life stuff for everyone.

Electronic equip hooked into the wiring, won’t cause the battery to spill acid. It could drain the battery but not boil it over while sitting. (If it’s draining the battery regularly, then the installation was done improperly.) After the new battery is in, if you go back to the battery installer, they can tell if the system is okay vs if something is problematic pretty easily (if they are at all decent). Just read the volts, resistence…readings will be normal or not.