Depending on the specifics of the circuit, you could get away with using a 7.4V Li-Ion charger on the pack leads. But, if the circuit board doesn't have balancing features, you'd need a balancing charger.
Doesn't look like there's any balance taps on that thing from what can be seen in that image, and the circuit board doesn't seem to have any power resistors it'd use to dissipate balancing power. I'd thoroughly examine how the pack and board is supposed to work (or not work, if it's just plain bad design), or examine the datasheet to find out what features the board has, and how the manufacturer intended for the pack to be charged.
Or, you could just charge with a current-limited 8.2-8.3V powersupply and replace the pack before it becomes too damaged from it and catches fire