Worked for......
A phone company for over 10 years.
Battery performance was one of the biggest complaints of handsets.
If you haven't already, here are some things to extend your battery life
1st - By far the biggest thing that drains battery, turn your screen brightness down as low as you can bear, also turn of "auto brightness" if convenient as you then have total control of it
- When you are not in range of any Wi-fi, turn it off, your phone will still scan for wifi networks, no point in it doing that if you cant/dont intend to connect to one
- Like wise, if you arent in range of any 3G/4G networks, you'll know this as you wont be able to browse the web, or the 3G/4G symbol next to signal indicator/network name will not be there. Or at best will show GPRS or E (which these signals aren't strong enough to run a data connection on a smartphone. Your phone will always try to connect to the strongest signal it can, so no point having it frantically scanning if you know you're in an area where there is nothing but basic call/text connection.
- Any apps you don't use, delete off the phone, if you have auto app updates turned on, the phone will do updates for any apps that need it, no point doing this for apps you dont use, as it uses battery, and even worse, uses your data allowance if the app updates are done on your mobile networks internet connection
- Turn off the feature that allows apps to refresh in the background. Go to Settings > General > Background App Refresh and set the switch to Off.
- Likewise, your email app, change this from push email to fetch email, this means instead of emails coming through automatically, you will only get new emails come through when you actually open the email app on your phone, as when it is set to push through, your phone is practically always scanning your email accounts server to check for emails, so it can bring it through to your phone.
There are other things you can do, but above is what I can recall off hand
It sounds like a right pain written down, but if you can do any of the above things, it will definitely extend the battery life, I do it of course and it is second nature now.
Lithium batteries (what are used in smartphones over the last 8 years or so), are much better than what was used before. They dont develop memories like older batteries did or degrade as fast. Even so, they will only go through so many charge/discharge cycles before their performance degrades and doesnt perform as well as it did. If you are still happy with the phone, you can take it to apple for the battery to be replaced.