Do what jolly said. Disconnect the batteries from everything. Charge each individually. After you unhook the charger, wait 1/2 hour and check the battery voltage. if less than 12.5 or so volts, the batteries are toast. Better is to charge them and take to auto parts store and load test.
Batteries should not be left unused for that long without being hooked to a charger/maintainer. By boat has an onboard charger/maintainer and the original batteries lasted 9 years and were still strong but i replaced them anyway just to be safe. And the boat sits outside in cold Kentucky winters, which is even harder on batteries.
Lead/acid batteries MUST be kept charged or they won't live long.
Good luck and keep us posted,