, or

Lead acids.
Have you checked to see it they come up with a reverse charge?
This is somthing that is quite safe to do to a Lead acid (but never a Nicad as they explode), as this is how the original batteries were made.
There is 2 type of lead (Pb) sulphate that is formed on flat batteries, the first type is conductive & allows normal recharging, the 2nd type is hard lead suplhate that just insulates the cell plate & inhibits normal re-charging unless very high voltages (>5V/Cell) are applied. But reverse charging (with a suitable current limiting lamp in series) will break down the hard sulphate immediatly. A couple of charge/discharge cycles will then bring back a heavily sulphated battery to near normal capacity.
DRY?? The so called dryfit batteries are actually wet types with a clever seal. They are just as susceptable to loss of water by overcharging & warm temperatures as wet batteries are, but your supposed to throw this type away instead of topping them up! However closer examination of the top of dryfits will show a glued cover over a set of 6 rubber cup caps that if removed will let the cells be topped up as normal. Only some success is possable with this method, as over charging usually destroys the lead frame in the +ve plate as well & it falls apart
Cycle charging up to 14.5V (6 cells), 13.8V standard infinite float charge, but 13.5V MAX on sealed cells.