The battery polarity is the same for 7R and 8R, and the charging
contacts are identically distributed. The 8R battery fits in 7R's
charger. So, it is feasible to use 7R charger for 8R. The only
problem is that because the 8R battery is thinner and its charging
contacts are about 15mm lower than the 7R's, the charging contacts
cannot reach the charging pins.
All you need to do is a very simple modification of the charger.
Disassembly the charger by removing the 3 screws (1 on the bottom
heat sink and 2 on the PCB). You can see that the end of each
charging pin is T shaped, keeping it from moving outwards. Remove
this stopper by either cutting or bending the T-shaped structure, and
then bend the charging pins outwards to make them about 3 mm far from
their original positions (don't make them too far outwards, or you'll
have problem fitting the 7R battery). Re-assembly the unit, and
you're done! Now the 7R charger can be used for BOTH 7R and 8R!
When charging the 8R, you need to elevate the battery by putting
something that is 15mm thick under it (I use an AA battery).
Using 7R's drop-in charger for 8R 
Linear Mode
