The mobile batteries can provide power to your DSLR or Mirrorless for several hours.

This battery system was used in the following time-lapse video. (https://youtu.be/OhKNAlLMO4g) The Relay converts 5V/2A (USB input) to 9V/0.8A (camera require). I purchased them in following links. 1) Coupler (genuine): Nikon EP-5B Power Supply Connector https://www.amazon.com/dp/B004FPQH5I/ref=cm_sw_em_r_mt_dp_U_LoCqCbN4HH7GC 2) Relay (relay of coupler and mobile battery): CASE RELAY CRUPS 110 * Conversion adapter for Nikon coupler is attached. https://www.tethertools.com/product/case-relay-camera-power-system 3) Mobile battery: Anker PowerCore 26800 https://www.amazon.co.jp/dp/B01JYL3IF4/ref=cm_sw_em_r_mt_dp_U_cgCqCbCK6NQ45 (You can't buy? Don't worry. Any other general mobile batteries must be able to work.)