I just got in a cheapo ebay USB to 7V4 Lipo charger with 3-pin connector for battery. I was hoping to charge a 7V4 Lipo battery in a handheld device that just provides a 2-pin connector to the internal battery (2 cells in series). Alas, it looks like the USB charger connects 5V to one 3V7 cell at a time and so separately charges the battery pack's cells, rather than charging the 2 cells in series (as per say a boost). A quick reverse engineer of the charger circuitry is below. Anyone have any ideas on the 14-pin controller IC being used, as some googling didn't show up this configuration of charger circuitry ?
I'll have to go looking now for a different charger to suit my device, but it was interesting to see what I think they were doing. Initial checking on suitable chargers seemed to show two forms of battery module - one form with two cells where the mid-point connected to the 3-pin connector, and another form where an internal thermistor connected to the 3-pin connector.