Zero One recommends players only use 9.6v NiMH batteries on AEG's that have been upgraded or that fall outside of their warranty period. The higher the voltage increases rate of fire meaning that 9.6v batteries are a popular choice with many players but it does mean that the gearbox will have to work harder and faster. For this reason 7.2v or 8.4v NiMH batteries should be used to maintain the longevity and reliability of your AEG.