This is suggested every once in awhile. See the many earlier threads on this. There is a mod that uses a 2AAA mag body, I have tested 2AAA with the head with no problems (the circuit limits the current) but brightness is only increased by about 50%, etc.
Peter -
how robust is the driver on the older Arc's?
I have an older red led Arc AAA head that rides on a short 10180 sized Peak black body. Currently, I'm running it with a small NIMH battery. I would really like to run it off of a Li-ion battery. Will the driver circuitry on the older AAA heads handle the 3.7V Li-ion battery?