In general yes, but if your jury rigging something, use a protected li-ion cell,
Also be aware that if they are using a charge managing IC like they do in some GPS's (similar devices internally), you will want similar capacity or you may hit a timer limit which means it never charges, if its just a generic charger IC, you could well throw a 2200mah 18650 in a socket on the back and have it last much longer.