A few battery tips garnered from many places. First check out battery university to better understand Li batteries. Also since most of us upgrade to new devices after two to three years or sooner, most any way you decide to charge and use your device will give you a usable lifespan. So no need to get OCD over your battery.
The batteries are rated for about 500 100% discharges and still have 70-80% of full capacity. Note that five 20% discharges equal one 100%. Also, as with all manufactured items, a certain percentage will get a bad battery and or device. No manufacturing process is 100% perfect all the time. If you get a bad one, go to Apple Store and see what they will do for you.
Li battery chemistry hates heat. So avoid high temperature situations as much as possible. If your device gets hot during charging or intensive processor use, try to allow contact with cooler surfaces to draw away heat when in these situations. Never leave your device in a hot car, even turned off.
Li batteries will fail if overcharged or if allowed to fall below a threshold voltage. Use only Apple chargers and cords as the device in conjunction with these is designed to prevent over and undercharge conditions. You may be lucky and use third party charger/cords without incident, but you really want to risk hundreds of dollars to save twenty bucks?
If you want to be kind to your battery, consider usually charging when you reach 30% and ending charge at 80%. This is a sweet spot for the chemistry of Li batteries. When it's convenient, and I reach 30-40% I connect the charger for short time, like 30 minutes and take it back into low 80% range. Of course when I know I need it due being on the go, I charge to 100%. I may be deluding myself, but have noticed increase in duration since I got my iPhone and iPad following this protocol. About very six weeks I will drain to 10% and charge to 100% to recalibrate the percent meter. Doesn't do anything for battery, just adjusts the range of the meter to improve accuracy.
I leave you with this to ponder. Toyota in their Prius Hybrid has the Li battery pack cycle between 60% low and 80% high. Since the battery pack is $10,000 and needs to last the life of car, five years plus. They use this conservative charge cycle programmed into the controller to maximize battery longevity.
Enjoy your devices, and don't be too stressed over your battery.
