My iPhone 6 battery life is so bad. Ways to improve it?

It's usage is 4 hours 33 minutes and the standby is 15 hours and 9 minutes. The battery percentage is 39

Added (1). I've been using my 4g 24/7.

Change it

The TIPS and the booklet from iPhone that you download to your phone will tell you how to fix this. You clearly have a TON of stuff running in the background, or on PUSH or auto-update. You can also Google for suggestions, because many good tech mags have excellent advice. I'm not going to type is all out OVER again for you - try using some common sense and investigation first, and then read up for more. I bet you can also clean up a lot of storage issues for yourself along the way, too.

There's no way that you can increase your battery life, but you could reduce your battery usage and for that you need Leo Privacy Guard. It has many advanced security feature, and its RAM booster feature would be useful for you as it can kill the unwanted running applications in a single click and eventually it will increase your battery life.