maxpro 2s lipo monitor. off the bay for aprox. 14.00 shipped to you. heli direct has them in their ebay store. Super nice quality. nice led's for visual and it beeps loud so you can hear it when going around the track. I have used these for a while and then gave them to friends when i went to newer speedos with cutoff built it. they are all happy with them.

http://www.helidirect.com/maxpro-bat...ies-p-8158.hdx

search lipo monitor on ebay too. that is wear i got mine.

ebay item # 360148783824 < the exact one i used. in the usa too
type that # in the ebay search bar
good luck