if its anything like the excellent 530, a pair of ni-mhys will last a long time.
2x1.2v 2000 or 2500ma batteries is a lot of juice to shove into a "compact" camera, many compacts use a li-ion with less total power, the ones that use 2x and 4x AAs do a whole lotta pics, and carrying spares is easy cheap and fast.
so i believe you will find that even a pair of enloopies (for intermittant use over time) or some good high-cap 2500s will give you all that you need , and having a spare is easy too.
18650s wont fit at all, wont be the correct voltage, and the 14500 li-ion rechargables will not be the right voltage either, even though they would fit.
i think you will find that the use of the simpelest AA rechargable will be awesome without any changes modifications or even high priced lithium cells.
look at how the battery container basically "sticks out" of the cam
they really thought about POWER when they made those models. (its a handle, no its power)
as your "spares" if you ever need them (more than 300 pics +flash) get some "LSD" cells like enloop, then they will stay charged longer in your bag.