You can use any battery with same voltage and higher amperage but size and weight will limit usage Ex.: 11.1*1300 ma I think is the limit for HBFP and HBCP mainly because of weight and size (maybe you can go up to 1500 MA but I think that it would add too much weight).
Of course you can use the Esky charger for any Lipo/metal battery but check the positive and negative to be equal on both sides (charger positive to receiver positive and charger negative to receiever negative or a short circuit will happen).
The 10 c 15 c and 20 c are the discharge rates which translates to more time charging the battery and more time discharging= more time flying and more money for the battery.