Make sure the charger port from the power bank, cig lighter doesn't exceed 2amps, the mod will take what it needs but no use having anything in excess. 2nd would be not to leave the batteries unattended during charging in case of a mishap. If they start getting exceedingly warm, unplug them for a bit to let them cool or direct an A/C vent down on them, you'll be battling the heat from charging and sunlight coming in from the windows.