Charging batteries is easy. You just use the shitty mobility charger that it came with, plug in till you get a green.
That works. ANYTHING works. But its all a matter of how well.
Apart from incomplete charging, causing sulfation build up, most mobility chargers and automatic one size fits all chargers charge at a too high 28.8 to 29.4V.
The CORRECT voltage to charge a gel battery would be a MAX of 28.2V (14.1V each). And a MIN 27.6V (13.8V). Or less. Thats at 20 centigrade. The battery may actually be warmer than your room. And the room may be 30 centigrade in summer...
The perfect voltage or best cycle life would be 13.95V or 27.9V charge at 20C. Or a MAX limit of 28.2V.
Not the typical 28.8 to 29.4V we see on generic gel/AGM batteries.
The difference seems small but...
Now take a look at this... Would you prefer 500 cycles or 300?