The Golden Eagle PEQ2 Airsoft Battery Box has a built-in rail system and already comes with a 10.8V mini NiMH battery! This 10.8V battery has a long battery life and is built from high quality materials. This PEQ2 style box is compatible with any airsoft gun with a railed handguard. It quickly and easily attaches to your rail system and features a side rail of its own (so none of your rail space is wasted), making it idea for compact CQB rifles! It also features realistic markings and is constructed from a durable polymer to prevent damage to the battery inside. Its polymer construction allows it to also be lightweight, which wonâ€™t weigh your rifle down or throw off its point of balance.