Can you share some advice on how to prolong overall battery lifetime? How many times a day should a phone be charged, from what percentage to what percentage should be the battery charged, any useful apps, etc. Thank you.
The usable capacity of a lithium battery is 40% to 50% of the capacity rating. Discharging it past 50% shortens the life. Down to 40% doesn't shorten it much. Down to 20%? You might get 2 years out of it, if you're willing to use a battery that can't hold much charge for a few of its last months.I wouldn't be too strict with this "do not let it fall below xy%" rules. Might be good to keep it in mind, but not as a strict rule. Because if you "never let it fall below 50%" you effectively cut down your capacity by 50% on day one.
If your battery loses capacity, just replace it. My N5's battery cost less than $15.
As previously mentioned, deep discharge is not a good idea if you want the battery to last a whilke. You should read Rukbat's post.Don't charge your battery again and again only charge in when the battery close to gone. This may help you increase your battery life.
My Xperia Z2' s battery is non-removable.