The Apple devices use lithium-ion batteries instead of traditional batteries since the lithium-ion batteries charge faster for convenience, last longer, and have a high power density for more battery life in a lighter package. Note that "battery life" is the time your battery will run before it must be recharged. Apple states that standby battery life of the batteries is one month.

The current generation of iphone lithium-ion battery uses a combined charging process:
        i) Fast charging to quickly reach 80% of its capacity in order to let you get out and about sooner.
        ii) Switches to slower trickle charging in order to extend the lifespan of the battery. Note that 'battery lifespan' is the amount of time your battery lasts until it needs to be replaced.

On the other hand, with the current generation of Apple batteries, the charging is very convenient:
        i) The batteries can be easily charged since they can be charged whenever you want. There’s no need to let it discharge 100% before re-charging.
        ii) The batteries work in charge cycles. You complete one charge cycle when you’ve used (discharged) an amount that equals 100% of your battery’s capacity, but it is not necessary to come from one single charge. For instance, you might use 80% of your battery’s capacity one day, then recharge it fully overnight. If you use 20% the next day, you will have discharged a total of 100%, and the two days will add up to one charge cycle. However, similar to traditional batteries, the capacity of Apple batteries still has a limited number of charge cycles and thus will diminish after a certain amount of re-charging.

For older generations of Apple devices with lithium-ion batteries, the charging was not so convenient. If you do not plan on using your device for more than six months, you need to store the battery with a 50% charge. If you store a
battery when it’s fully discharged, it could fall into a deep discharge state, which renders it incapable of holding any
charge. On the other hand, if you store it fully charged for an extended period of time, the battery may experience some loss of battery capacity, meaning it will have a shorter life.