I would recommend you top off the batteries with distilled water, then
connect a trickle charger for several days. A standard flooded cell lead
acid battery will quickly regain about 85% of capacity, but the balance of
the charge is accepted in the "absorbsion" phase, and can take 72 hours or
longer to reach 100% of capacity. You may also want to jostle the batteries
a bit during this time to release any bubbles formed on the plates, and to
stir up the electrolyte as it tends to stratify when batteries sit for long
periods of time.

Good Luck