i put them on the case so i can store them somewhere without losing them.If Li-ion battery is used, then that doesn't affect battery life. Actually, if you use earbuds very rarely, then you don't need to charge them all the time (assuming earbuds have physical off switch) -because Li-ion batteries don't self-discharge much over the time.
they are li-ionWhat type of battery do they use? Even then it depends on how the charger has been configured. Li-Po batteries do not like being stored at 100% however the charger may give you 100% reading before the cells actually reach 100% charge. Li-ion do not mind.