Your chances of recovery depend on how long they've been flat for. With lead acids when they're discharged for a long period of time the sulfur in the acid falls out of solution and ends up forming an impermeable layer of lead sulfate on the plates. When this occurs the only real way to fix them is to melt down and remake the plates.
As for recovery charging you really need a manually controllable charger with a constant current mode.
General rule of thumb is to charge with the current limited to 1/10 of C1, ie: 8 amps for an 80AH battery until the battery voltage stabilises (usually around 17v for a 12v battery) and then charge for a further 8 hours. This technique will boil the battery so make sure make sure you follow necessary safety precautions that take into account hydrogen venting and potential acid spill.
SAFETY SHIT!!!!!!
NEVER use this technique on a sealed battery! It is only suitable for use on fully vented or valve regulated lead acid batteries.
The battery WILL vent hydrogen gas and potentially acid so make sure you charge in a well ventilated area or use appropriate extraction and NEVER leave the battery installed during charging.
Always check electrolyte levels (in vented wet batteries) prior to charging and top up with distilled water only, you can correct the SG after charging if needed.
TL/DR
Don't be a dumb ass when charging batteries or you'll blow your shit up!