http://cgi.ebay.ca/2S-6S-RC-Lipo-Bat...d=p3286.c0.m14
paid mine 6$CAD total in an auction on ebay. You can keep it plugged while you play! Show total voltage and individual cell charge.
it takes10 secondes to check or if you are really lazy you can read it through the handguard holes

Its probably the same as yours m102404
Heres what it looks like in a m4 handguard: