Common bead thermistor, used to sense the battery temperature to allow the charger to stop the fast charging when the battery starts to heat up when charging is finished.
Most likely a NTC type, probably a 7k at 25C one. Measure the resistance of it, it should be in the range of 2k to 10k at room temperature. Probably RS stock no. 697-4522 if it is around 6-7k at room temperature. Those are cheap at around 1 euro each from RS.