Howdy from Wyoming @valgriffiths , welcome to the community, plenty of fine folk and excellent information here.
Thanks for your feedback - I suspected it would be a bad idea but that is very useful to know re the voltage. I was just curious re a lighter option for charging accessories whilst travelling. Thanks a lot.No - that will not work at all. The adapter takes the battery voltage and drops it to USB level (5 V) to use as a source to charge or power USB devices. Trying to reverse that - i.e. feeding 5 V back to the adapter - will have no useful effect at all because these circuits are not reversible and the adapter will not convert the 5 V up to a level that would be able to charge the battery.