Is there a "best" way to charge your cellphone battery? Are there things that you can do that will make your battery die sooner? How many cycles can your battery be recharged before it needs to be replaced?
Be prepared to learn a thing or three about how to care for your battery and be prepared to have at least a few rechargeable battery myths dispelled. All of this information comes from BatteryUniversity.com, a free informational website that is sponsored by a manufacturer of battery packs, chargers, and battery diagnostic devices.
Most lithium-batteries have a rated lifetime of somewhere between 500 and 1500 charge cycles. One recharge cycle is any time you hook your phone up to charge it, regardless of how much charging is actually done. The depth of discharge (how much energy is recharged) is a big factor in determining how long a battery will last.
According to Battery University, a li-ion battery that goes through a 100% depth of discharge (the battery is run down to zero and fully recharged back to 100%) can degrade to 70% of its original capacity in just 300-500 cycles. In contrast, by keeping the depth of discharge to 25% (running the battery down to only 75% before fully recharging) you may be able to lengthen the battery life to 2500 cycles before it starts to seriously degrade.
If somebody tries to tell you that the number of times you charge your battery are the primary factor in determining battery life without considering depth of discharge, they are mistaken.
Were you around when ni-cad batteries were a thing? Ni-cads were notorious for developing "memory". If you regularly recharged a ni-cad when it was still at 50% capacity, over time, you could end up with a battery that only hold a 50% charge when it was fully charged. Only nickel-based batteries are susceptible to memory, memory is NOT a problem for lithium-based rechargeable batteries.
Lithium-ion batteries don't like heat. Exposing a li-ion battery to temperatures of 100 degrees F for a year will cause it to lose about 40% of it's overall charge capacity. At 75 degrees F, a li-ion battery will only lose about 20% of its overall charge capacity.
Contrary to popular belief, leaving your phone or laptop plugged in all the time is not bad for the battery. Modern chargers are usually quite smart and know when your battery is full. When your laptop or cellphone battery is full, modern charges will change to trickle charging - charging at low "speed". Trickle charging is much less detrimental to the life of your battery than deep discharges are. It is probably a wise idea, however, to avoid cheap chargers and stick with the charger that your manufacturer gave you or use chargers from reliable aftermarket brands.
Running your battery down to zero doesn't really mean that your battery is completely empty. Lithium-ion batteries become very unstable if they are discharged completely. Sometimes, discharging a lithium-battery completely can result in a fire or small explosion. Due to this issue, most lithium-ion batteries have an internal protection circuit that will trip and kill the battery permanently if the battery is discharged to an unsafe level. This prevents the battery from discharging to a point where fire or explosion becomes a possibility.
If you have a removable battery, the most important sign to be aware of is when your battery starts to bulge. Lithium-ion batteries are powerful, but they are less stable than other types of batteries. When lithium-ion batteries begin to fail, they produce a small amount of flammable gas. This can obviously be dangerous, so lithium-ion batteries are also completely sealed and designed to contain this gas.
When this gas builds up, it will cause lithium-ion batteries to bulge and expand. This can cause the battery to rock back and forth in your phone and randomly shutdown because the battery terminals lose contact with your phone.
I'm not trying to scare anybody. It is POSSIBLE for lithium-batteries to explode or burst into flames and if you look hard enough, you will find stories about situations where this has happened. Lithium-ion batteries and their chargers are VERY safe. I have been using a cellphone with a lithium-ion battery for years, as have most of my friends and relatives. Nobody I know has ever owned a battery that exploded or caught fire.
Even on an expensive phone paying somebody to swap out your battery will probably cost less than $70 and a new battery may allow you to keep your phone for another year. That's a good deal if you ask me.