I'm going to take the plunge to take apart my One (M8) to replace it's battery tomorrow and I was wondering what I should do to increase its battery life right off the bat. Should I charge it to full capacity first then use it normally, charge it to full then drain it and recharge it, or does none of this matter?
The reason why batteries degrade over time is because blockages build up in the individual cells as the current passes through them, preventing them from fully charging. This is a chemical process and is unavoidable, but one thing that is sure to speed it up is extreme temperatures. Too hot and the reaction speeds up. Too cold and the phone eats up all of the power to warm the components.
So here is a few helpful tips for keeping your new battery happy:
- Keep your phone off of any insulated surfaces when charging
- Turn off background processes that can make your phone run hot
- Turn off features that you aren't using or don't use frequently (Bluetooth, location, even turning off wifi can cool down your processor)
- Keep your phone close to your body in cold weather
If you are concerned about the length of a charge, some of these tips can help there too. There are also free apps that allow you to manage the processes running on your phone, clean up junk files, and boost the efficiency of the apps you are currently using. There are also some cheap apps that allow you to modify several aspects of the OS without needing to root your phone.
As far as charge frequency, you should be fine regardless of what you do.
When the phone is marketed, manufacturers, typically charge the battery to around 40% as you may have noticed. This is good for battery longevity and ensures battery degradation does not occur on storage. See BU-702: How to Store Batteries for better understanding
There isn't a valid reason for charging the batteries for xx hours before first use or to charge till 100%. It is yet another charging myth , see misconception # 6
See BU-415: How to Charge and When to Charge? for a general understanding of charging "do's and don'ts)
Additional information on this site that would help you care for your batteries