Sounds like the cure is a Louisville Slugger - just kidding.
If you have battery fill system on all your batteries - I would think that over filling would be difficult. Often "boiling" over is caused by too large (amp capacity) of a charger being connected to the battery or incorrect volt charger being used (e.g.. 48 volt charger - 36 v battery) - either situation will cause excessive gassing will take place and force the electrolyte out. I've seen situations where the tabs on charger and or battery connector half have been broken out & allow a different voltage charger to be hooked up.
Just a thought or two from here at least 700 miles from your problem but only milliseconds via the internet.