You will have to be able to disconnect every cell past 8.4v to charge your pack, because using only say 7 cells in a 10 cells pack, you will get a different discharge in your first 7 cells, and charging the pack as a whole will destroy the remaining 3 cells in under 20 charges.
Plus, if you start looking into C programing, you will see that the changes you have to do to the trigger master program are not that big.
You can use a multi switch, like the ones on old sound systems to change input/output. Wire each switch with a different resistor and compare each voltage with the PIC. You only need to use 1 analog input on top of the regular digital input used normally.
You could even use a potentiometer and simply use it as a PWM control over the PIC's output. That way you could control percentage instead of steps.
Hell, you could use some 14.4v packs in there.
11.1v is the best voltage to use since most CMOS based chips are referenced to 12v.
here is the link to some packs. There is a whole lot more out there. If you are looking for safe packs, check ROAR's authorized packs. They send the packs through extreme tests, including over charge/discharge, NiCd charger, drop, perforation etc.
They are not making 5000's in hard cases, but these are the size of a 7.2v Sub-C pack.
You can get many 5000+ packs for airplanes and helicopters.
http://www.teamorion.com/Products/SL...Platinum+SLPB+
Here is the link to ROAR's website:
http://www.roarracing.com/approvals/lipobattery.php
All these packs are known safe to every extend. You can drive a nail in them and not worry about your hand been removed.