If your panels are 6v and have an output of 1a or so, then with a series diode you could connect them direct to the battery.
If they are a higher output then you'd need a solar charge regulator.
That said, if the batts are lead acid, or nicad etc and they've been lying around for months, they are probably knacked, if you dont use them they go flat, and if flat for long periods loose capacity.
If you cycle them a few times with a mains charger they might come back.