RE: field charging lipos
I have the same issue with power at the field, so I have six packs, fly all of them and then go home.
In the WC in Portugal, the electric guys had the car engines running all day long to power the charges during practices, it is simply easier to use the car than transporting bulky/heavy charger/batteries setup in my opinion. Chinesse batteries will work good to as JClaude suggested.