The
cells I am using are rated 3.0V and therefore are charged at 3.6V and not 4.2V like the normal RCR batteries. There is a
3.0V Nano charger available identical to the normal one and you must be very careful to properly identify it (red pen etc.) so you don't use the wrong charger.
Since the charger is meant for CR123 size you need a small spacer/stack of magnets with the CR2 cells.
As it is usual with these brands, the capacity written on the cells is pure fantasy. You may find several different markings but the figures are unrealistic. The ones I use are probably 400 mAh since the runtime is approximately half of the one of a primary.
Remembering that RCR2 batteries are not protected you must charge them regularly and quite often.