Use Any Battery
If you simply make an adapter cable you can quickly connect your most common batteries without ever doing it wrong. I use a 3S balance connector and a an old servo lead to make an adapter. 3S balance lead extenders are really nice for getting lipos in a lipo bag and are available cheap on ebay. Cut one an use the side that connects to the battery. Solder it an old servo lead or use the male half of a servo extender or you could just solder female half of balance extender directly to power pins on tester. I also have several old futaba NiCad receiver packs from 30 year old 72MHz radios that still work fine and mainly use those now that i finally found them. The adapter I made is a good back up method now. Adding a fuse to the adapter will protect everything somewhat and be a lot safer.