The included charger will bring the battery up to it's full capacity either to the 1600mAh or the 1000mAh, so there you are safe from overcharging.

By putting it on a discharger you can see how much current has been put into the battery.

To play it safe, charge the battery fully.

Put it in the plane then run the throttle up to about 80% while timing how long it takes to hit LVC.

This will give you a fairly accurate estimate of run time, and also give you an idea of battery capacity.

If you post your results we can estimate the latter and see if the battery is indeed mismarked.