There are 3 main types of batteries; nickel cadminum (NiCD), nickel-metal hydride (NiMH), and lithium polymer (LiPO). NiCD batteries were one of the first batteries to be used in airsoft. They are available in 8.4V, 9.6V, 10.8V, and 12V packages with varying mAh ratings. NiCD batteries are not as common as they used to be in airsoft due to the fact that they have to be completely discharged before they can be recharged again. This axtra step can be an inconvenience, even for those with smart chargers and dischargers. It is for that reason that NiCD batteries are phased out of airsoft, however you will see some for sale every now and again. NiMH batteries have been replaceing NiCD batteries since they are offered in the same voltage and mAh as NiCD batteries, except NiMH batteries donít need to be discharged before recharging. NiMH batteries are currently the mosr common type of airsoft battery. Itis a lightweight and very powerful battery pack. LiPO batteries are commonly offered in two voltages, 7.4V and 11.1V. Many of todayís airsofters are swiching to LiPO batteries because they offer more voltage than NiCD or NiMH batteries but tack up far less room. Higher performance from a lighter and smaller package would seem to make NiMH batteries completely pbsolete. however there are still some that prefer the more stable NiMH batteries to the more volatile LiPO batteries. lituium polymer batteries can be dangerous if mishandled, which is why Mars Battery onle sells LiPO batteries with the proper charger and a LiPO Sack.