Ice cold batteries
Bought a new phone battery and it is losing charge within weeks? Then you can try keeping it in the refrigerator. Sounds odd but it is true. Most of the smartphones use lithium ion batteries that get exhausted because of the heat generted during their use.
Keeping them in cold environment not only extends their life but also increases their power. But make sure that the batteries are wrapped in a poly bag or a zip lock bag while they are inside the refigerator.
The other simple ways are by turning off screen's auto-rotate function, Bluetooth, reducing the screen brightness and GPS. If you are not really bothered about using the Wi-Fi and have an internet pack activated, you can switch off the Wi-Fi as well. However, if the problem still persists, it is likely a software issue and you must take your phone to a technician.