Your TV will display a low remote warning when the charge on your remote control battery gets to 10%. You can check your remote control power level from Settings> Remote.
Use the charger and charging cable (micro USB) provided with the unit to charge your remote. The charging port on the remote is at the bottom of the remote.
Using the charger included with your purchase it will take approximately 2.5 hours to fully charge your remote. With normal usage the remote battery should last approximately 4 months.