If the rechargeable cells are a similiar size to the 123, the cell capacity will probally limit the voltage to quite a safe range for the LSH. Under load, it is best to keep the battery voltage below about 3.4v. Smaller batteries sag under a heavy load so the actual voltage is then in a safe range.
This same effect works in the coin cell lights. You have a 6volt battery that runs the LED at 3.8 volts under load.
Peter
