Portable Power Source

[Mike_D]

Hey guys i have not been on here in a long time. I took break for a couple of years. Well now i'm back in and have picked up a couple of electric 1/8th scale buggies for my son and I. Anyways i'm looking for a portable powersource for charging some 4s lipo batteries at the track and i don't want to haul around a gas generator. Does anyone know of a portable battery or source that i could charge at home and then take to the track to able charge my batteries? Does something like this even exist and if so what would i be looking for as far a specs?