Semester 2: USB battery pack

I decided that instead of fixing into my table a USB multi port with a socket underneath the table for power supply, I'd make a pocket in the table top that fits in a USB battery pack. This will remove the cord previously required, which was an unsightly tripping hazard, add functionality, and give the table a modern 'smart' feel. This will be a hugely useful function IF the students leave their tablets at school for the teacher to charge over night. If the students take their tablets home, they will look after charging their batteries, but there is always a chance of them forgetting, again making use of the battery pack.

I need to find out how many tablets are used per table.....is it one per student (6 per table), or do several student share one? And at the end of the day, the teacher wont leave the tablets charging on the table, where they're visible to burglars. I imagine the teacher will move them to a shelf, where there are numerous chargers plugged into a wall socket. But do the tablets need a full charge after only an hour or so use? Will a battery pack be able to top up several tablets from around 60% battery? So many questions! I'll email around and get some insight from teachers as to what specification I can build this table to.