Most Power Banks on the market today are 5V so would work fine. We recommend 10,000 mAh for a full 12 hours of power, but 5,000 can work if only around 6 -7.5 hours is needed at a time. One think you may want to look for is a battery that two USB out ports so that you can use it to run both your Ever Sip™ and another USB powered heating device like gloves, a vest, hat, etc. Here is one we have used and can recommend if helpful - Anker 10,000mAh PowerBank with USB-C and USB-A Output
Power Bank Specs should be within this range:
Minimum: 5v and 1A = 5 watts
Maximum: 5V and 3A = 15 Watts