Open Geforce Experience, choose preference window (should be the last one) and there you should see "BatteryBoost" in the left panel. You can disable it by unchecking the first box.
Anyway, remember that your laptop won't reach the full power due to the power limitation, but you should reach more than 30fps in Overwatch anyway.

Firstly you shouldnt game on battery. Every depletion of the battery is less lifespan it will have. Often the brick alone does not have the power to run the grahics so it draws on battery to make up the difference. The battery does not have anywhere near the current delivering capacity of the brick. Near as I can tell by the specs provided (lacks C rating) its less than half.
88 watts from battery vs 180 watts from the brick.

Hello BL_11
It's recommended to game while plugged in in order to have the best performance and to preserve your battery life
Thank you