Quote Originally Posted by barkerben
hmm...I have found a 3.6v regulator. It can supply up to 1.5A, which I hope will be more than enough. The GSM module specs is a bit vague - it says consumption is <350mA when transmitting data, with peaks of <2A. Should do the job... and I can run the regulator off 4 AA cells.

:-)

OK. That will work, but if it is a linear regulator, it dissipates the difference voltage in the form of heat, and is very wasteful. As far as lithium rechargables, they have a very flat discharge voltage until they are out of gas. This might be your best bet as you can lose the regulator all together. Look at the Maxim website for switching regulators. I would personally use a boost regulator with a couple of alkaline "C" cells if you have the room. I have also used two pairs of AA cells in parallel. Maxim has a couple of small regulators that will put out up to 3 amps until your batteries have been drained to under 2 volts (deader than dead?). With all of the switchers, noise is an issue. Shielded inductors and low ESR caps are a must. They are fairly easy to work with and maximize your battery life.