Hyperion EOS Sentry Battery Checker Great for checking packs before use and after charges or before storing. Shows at a glance the remaining capacity in your battery pack, cell balance, and other information you need to get the best performance and reliability from your batteries Works wth most battery types on the market. Thunder Power packs require an optional adapter plug (purchased separately) Works with Lithium Pack Sizes 2S-7S, NiMH and NiCd 4-7 cells.