Originally Posted by gbjbasdw
There is some circuitry in the USB plug itself. A red LED turns on when the battery is charged so there must be something inside the USB plug I would assume.
So any ideas if the PCB on the original 5888 battery would be ok to use in say a 250mAh battery as well ?
Yes there is some kind of circuit in the USB plug, but it is not a charging regulation circuit. I think it's just a circuit that senses when the battery is at full charge ... meaning the charging voltage has increased to near the max allowed for a LiPo, which is 4.2 volts.
Many here have proven that the USB charger does not have a regulator because they have used it on a LiPo (the BestOfferBuy 6010 clone) that does not have the circuit board on it, and the result was a puffed up, over charged battery that was toast.