On a Tellur 30.000 mA (https://www.tellur.com/product/30000mah-compact-power-bank/) it works arround 20 hours at 0 C degree, and 26 hours at 15 C degrees. Its ok if you buy 2 or 3 powerbanks. My camera stay allways on powerbank (even if I drive) and when I park, the camera enter in parking mode...