Curiosity got the better of me and I broke into an older Sony L mount battery labeled 7.2V 4600mAh.
This one dated 10/2005.
Lo and behold, the 18650 cell shows up again.
This pack is configured as 2P2S. 2 cells in parallel with 2 in series.
The upper strap is the center tap, where the +/- come together.
From this configuration we can conclude that the cells are rated at ~2300mAh each.
On the nominal side of the rating for today's cells.
This configuration would yield about 33Wh.
The business end of this pack reveals the PCB which provides various functions that might include overvoltage, undervoltage, and short circuit protection.
This circuitry might also perform cell balancing on recharge.
The C terminal in the center communicates battery status.
So, without destroying it, we can deduce that the larger 7.2V 47.5Wh battery is the same 18650 cell configured as 3P2S.
Indeed 1/3 larger.
Careful surgery might allow replacement of the lower rated 2200mAh cells with cells of current manufacure that could produce 2800mAh.
This would give us about 60Wh, right at what our favorite Lenmar packs are giving us.
So without the addition of another parallel pair of cells and the increase in case size, we seem to be at the limit of the L mount capacity until another cell density improvement occurs.