im going to buy a CA m15a4, how long do the batteries normally last
Typically, it's about 1 shot per mah rating of battery pack and using an M100 spring. But that's all dependent on condition of battery pack. I have had very good results with the G&P battery packs and of course Sanyo packs. I haven't had any good experiences with "generic" packs but I know others who have. I believe some on this board have purchased packs & cells from onlybatterypacks.com. Then just use a $25 RC car charger.