I don't want to ruin your sale, but these boxes are probably left just good for the box it is, when the circuit board goes, it drains the batteries, and that's a problem for LiPo, especialy the not so expensive ones.(I hope yours did survive that experience, but only opening the box, removing the PCB and messure the battery will be conclusive)

Ilyama is replacing the innards of such a box for my recumbent tadpole Streetfox with 4 5S 5000mAh Flightmax LiPo's and balancing/charge leads. A Quad Charger will do the rest.