Battery C Size measures 50 millimetres (1.97 in) length and 26.2 millimetres (1.03 in) diameter. So the Tek Battery pack is about 20cm with 26.2 mm diameter.
A 25500 Liion Battey is about the same size as a C cell.
How about then 3x25500 in series... will the 12,6V burn up everything?
Probably yes...
I found some 25500 with already the BMS integrated which is nice...
One questions... with 8,4V how much current does the Scope need?
I mean at 4,8V it needed 1.2A when full on (with backlight)... so at 8,4V maybe 1,2A*4,8V/8,4V=686mA? Probably yes..
wait with 12VDC on the charger jack it need about 500mA with no batteries attached... so probably it needs about 6W-5,8W (with backlight on!!!) to operate... the rest is just math...
So quick battery life check:
2 18650 in series 3100mAh (SMdude mod)
3,1Ah/5,8W*(3,6V*2)= 3,84h
2 25500 in series 4000mAh
4Ah/5,8W*(3,6V*2) = 4,96h
3 25500 in series 4000mAh
4Ah/5,8W*(3,6V*3) = 7,44h
Now since according to my old post the 4 C-Size cell are lasting 2,96h you will get 3,84-2,96= 52 minutes more with the 2x18650. Which is nice, but I personally think it is not worth the effort unless you really need the quick charge feature.... and all the Liion bat goodies.
Much more interesting are the configurations 2x25500, and the porno dream will be the 3x25500 (it will last probably one business day and then the night comes where you will charge it)...
EDIT: a 26650 size is also very interesting.