Make sure that there are no issues with you wall outlet, charger or battery.
Plug the phone in and check if the phone vibrates briefly immediately after it is plugged in, and the battery indicator on the screen changes from grey to green. If these things do not occur, check the wall outlet by plugging in another device.
If the outlet is fine, check if there is damage to the charger. Look at your cord and converter. Are there any cracks, delaminations, or frayed wires? These may be indicators that you need to replace your charger.
Another reason may be that your power settings may be set to "Enhanced" rather than "Balanced", which will cause your battery to drain faster by being at its brightest screen setting and using its max power output for your applications. Applications that use a lot of power may also be open, so close your applications when you are done with them to conserve battery life.
If none of these solutions work, you may need to replace your battery as it is defective or at the end of its useful life.
For more information on this issue, check out the trouble shooting page for a short battery life here:
Xiaomi Redmi 2 Troubleshooting