The lipo battery is the norm for most airsoft players out and there and for good reason.
There often smaller, lighter, take less time to charge and can often give better performance than there older NiMH counter part.
Just keep in mind they can get warm when charging so please don't not leave them unattended and on anything flammable.
Oper8 airsoft Lipo battery for sale from Leicestershire Airsoft
Leicestershire Airsoft is a Leicester based company
Leicestershire Airsoft offers UK delivery