You will need to make absolutely sure you won't fry your altimeter/timer outputs with a high current battery. The current Featherweight altimeter product page says:
- Four 25-Amp outputs compatible with batteries from a single Li-Poly cell to a 16V pack.
As far as I know, those are the highest rated outputs of any of the regular altimeters. Plus it has very sophisticated programming that you can apply to your staging output to help ensure it fires at the right time. Note that if you add a RockeTiltometer 3, it is limited to "Max 12.5 volts DC @ 12 amps for <2 seconds, non-inductive load". A 3 cell LiPo should work for the vast majority of ignitors, if the combo of C rating and amp hours gets you to what your ignitor needs.
For your usage, a 3S, 45C, 450mAh battery will output a max current of about 20 amps, (unless I messed up my math). So that would prevent you from overloading the outputs and should still fire most ignitors. From some testing I did several years ago, I recall the ignitors I was using needed about 8 amps to fire, but that was using a 4C pack.
The real take home message is you need to know your electronics, your ignitors, and your battery.
Good luck,
Tony
PS: The way C ratings work for LiPo batteries is you can take the rated mAh of the battery and 1C = output amperage. So a 1000mAh battery rated for 1C will output up to 1 amp of current. That same battery rated at 40C can output up to 40 amps of current. Some batteries have two numbers, one for sustained draw and one for surge current. LiPos with low C ratings will often have a small circuit board that limits the current to specified rating. The ability to dump huge current is one of the things that makes LiPos dangerous to work with if you have unprotected connections.