These will check the battery under a load similar to that of servos in use, and give you a good idea of your battery power. http://www3.towerhobbies.com/cgi-bin...?&I=LXWDZ5&P=7 It is a must for any field box.


Another nifty device that is often recommended and they do work well is http://www3.towerhobbies.com/cgi-bin...&I=LXHDJ2&P=ML.

The voltwatch is optional but for sure invest in the expanded scale voltmeter. These devices will save planes.