The batteries are ok if you don't run them down to 0%. What I do is use it during that day and leave it to charge over night while I sleep.
While there is no need to bring the battery down to 0% it is a good idea to do so once and a while. I only do it maybe once or twice per year on purpose and then it happens on its own a few other times just from me being away from a power source or not having the charger with me while I use it all day.
The reason for doing this is that those electrons in the battery that don't ever get used just sit there and over time may not flow out as well causing the battery not to last as long as a full charge should last. A full discharge and recharge gets new electrons flowing into the battery. So its not something that is permanent, a discharge and recharge should clear out the old electrons.
I wouldnt worry about the battery, its covered for a year by apple and they will replace it if it starts to not old a charge for as long as it should. You also have up until the end of that year to purchase their 2 year extended coverage. I never get the 2 year coverage plan because I always end up buying the new model with better features each year.