My venture in recycled Lithium battery packs has now brought my attention to the electronics hidden inside those expensive energy bricks.
A positive discovery was that if the battery pack circuitry is fed enough voltage (i.e. higher than pack fully charged V), cells get charged and balanced. Even without a computer attached. Cool! This means I have a balanced charger for 4s(2p) packs. At 14.8V they are too much for the FT-817 (even 16.8V at full charge!), but some uses would eventually come up.
Further inspection of the electronics led me to the datasheet of the charger heart chip: TI's bq2060. Reading the 59 pages datasheet here-and-there, it turns out that the chip is a smart charger that knows the whole history of its companion Li-xy cells. Not only it charges and balances the pack, but it keeps it in shape during storage and offers a lot of telemetry information like remaining energy and time, number of charge cycles, ... All this is achieved with a plethora of configuration parameters stored in an attached EEPROM.
It is possible to communicate with the chip and, if it is not locked, to review vital cell information (to make it look as new), but so far I have not found someone who shared the code for Arduino or in BASCOM-AVR or C. Not worth the effort writing my own, anyway.
Now what? While I wait for the 2s/3s charger to arrive I will try out this electronic "device" and recharge a DIY-assembled 4s2p Li-ion pack out of it. At least I will be able to evaluate the actual remaining capacity of what I've got (for free).