It appears that we have hijacked this thread from accolades due to Lynn for his new battery box to discussions about what is inside that box

I'll add one more related to the gel cell units being doorstops. I saw a recent tech tip that pointed out that a gell cell, including AGM's, can drop to around four volts across the terminals, and older style chargers will not even recognize the presencde of a battery in the circuit, and will not switch on the charging amps. The tip was to "trick" the charger by placing a charged battery in parallel with the dead gel cell, + to +, - to -, which will be recognized by the charger. After an hour the good battery can be removed, and the charger will continue to service the gel cell. It does not always work (some are truly junk ) but sometimes you may win! The real fix is to leave a Battery Tender on it when idle.