I am pretty much of a newbie with electrics.

It was suggested to me to use either 10 cell NIMH or a 3s Lipo with these motors:

Mega 16/20/2 5:1 gearbox

MP Jet 25/35 3:1 gearbox

I have a chance to get a new 4s lipo very reasonable. Would it be safe to run this battery with either of these motors, or am I going to burn them out due to excessive voltage?

I can not find anything definite on voltage/max cells for these motors.

Thanks.

yep, you can use a 4S lipo. However, your gonna need a dedicated lipoly charger. You can not charge these batts on a regular nicad/nimh charger. And, you must, I repeat, MUST have the correct voltage set on the charger. Each lipo cell is 3.7 volts nominally. So, a 4S pack is
14.8 volts. Another point, charge the lipo packs at 1C. This means, if your lipo pack is 2200 mah, the charger amp setting is 2.2 amps which equals 1C.
Last thing to remember. Pay attention to the discharge rate of the pack. If it is rated at 20C discharge, then the 2200 mah pack can be discharged at 20 times 2200 mah or 44 amps. That would be the max pull out of the pack. You should have an amp meter to check the amps being drawn by what prop you intend to use.

Dave...

OK. Thanks for the info.