the thunder power batteries have a different balancing plug.
you will need to make or purchase an adapter or cut it off and wire up a new one to standardize between your batteries.
as far as I can tell, the one negative pin is just spaced out one more on those connectors.
the purpose of the balancing is because each individual cell should never exceed about 4.2v's or it can actually cause the battery to combust. fully charged should read 12.6v's on a 3 cell. without balance charging, it might over charge one cell to an unsafe level.