If they are totally dead they're most likely toast. You can try to recharge, but I'd guess they won't keep a charge for any length of time.
If you had the switch in "store" mode that bypasses the converter so no charging will take place. Even with the switch in "store" it doesn't totally disconnect the batteries, the best option to disconnect for storage is remove the negative cable from the battery that goes directly to ground.
As mentioned top off the cells with distilled water, the chassis battery is probably maintenance free so no where to check it & try charging them or take them out to your local auto parts store to be load tested.
If by chance your dealer cheaped out & used marine type batteries that has CCA, MCA or CA listed on them those are hybrid batteries used for starting boat motors, not for rv use, they will not hold up to the constant charging/discharging in a rv.
Danny & Linda
Sold our '13 Thor Redwood 36 FB
Currently RV & truckless