i think you'll find getting the batteries back in shape will probably fix your issue with it.
If they sit too long they loose charge, sometimes you can get them to charge back up, but sometimes they just die and have to be replaced.
I would put a trickle charge on each one and bring it back slowly.
You can do each one individually or in pairs , how ever you wish.

Just make sure you mark the cables so you won't get them out of order of connection.

Once you get them charged back you can come back if any other problems arrise and work out those problems then.

good luck