There are at least 3 different balance plug systems
Fortunately the most common is used by Sky LiPo, Turnigy and most of the other "economy" brands. This is the wider pin spacing with ground followed by each successive pin adding 3.7v (nominal)
This one will direct fit the balance port on Turnigy, Hitec and many other chargers.
The error with your little voltage checker was probably just plugging it in reversed. This doesn't hurt most of the checkers of that style. If it was one that can be damaged by plugging in reverse you would have smelled the smoke quickly.