Compare energy in Wh. A 10,000 mAh bank rated at 3.7 V stores about 37 Wh, and conversion losses reduce what reaches the device. Choose capacity and weight for your trip. Check USB PD or PPS, output wattage, the cable and how power is shared across ports. Check input wattage for recharging the bank itself.
Buy from a traceable seller and check applicable local markings, protection features and warranty. Stop using a swollen or unusually hot unit. For air travel, check the airline’s rules for Wh limits and carry-on placement.