Hi Tommy,
It sounds a lot like something in the charging circuit got damaged in the drop and now the battery is no longer getting charged.
Although it's possible something on the motherboard got damaged, that's low on the list of probable causes here. Much more likely is that either the lightning port assembly or the battery needs to be replaced; without opening up the phone and doing some fairly sophisticated electronics debugging it's difficult to say which it might be.
If you're interested in trying to fix this yourself, I'd suggest buying a new battery and a charging port flex assembly. Open up the phone and swap out the battery (without gluing it down yet) and see if the charging works at that point. If not, the next step is to go ahead with replacing the charging port flex and retest.
Otherwise you could try taking it to a repair shop for an estimate; they may be able to give you an idea of what's wrong with it and how much it would cost to repair, but of course that's going to depend on their level of expertise and what kind of problem they find.
If you want to do the repair, I'd suggest ordering a new battery and charge port assembly. Check the battery and verify whether it comes with the battery adhesive; if not you'll need to order that as well, plus I'd suggest getting a couple of sheets of the precut adhesive for the display; they're kind of easy to mess up and having a spare means you won't have to wait while you reorder if it doesn't go right the first time. You can buy all the parts you need right here on iFixit, or they're readily available on sites like Amazon, eBay and AliExpress.
iPhone 7 Lightning Connector Assembly
iPhone 7 Battery: Replacement Part / Repair Kit
If you get them here, I'd suggest buying the Fix Kit with either one of those parts; that way the display adhesive will come with it along with all the tools needed to do the job right.
Again, my suggestion would be to replace the battery first and test to see if that's all it needs.
iPhone 7 Battery Replacement - iFixit Repair Guide
Don't glue the battery down; just plug it in, reconnect the screen and test and see if it charges. If not, unplug the battery, remove the screen again and proceed with the lightning port replacement.
iPhone 7 Lightning Connector Assembly Replacement - iFixit Repair Guide
You should be able to pick right up at Step 29, the speaker assembly, and continue through to the end of the guide. When you go to put everything back together, do the reassembly in reverse order, stopping after Step 29 and switching back to the battery guide to finish.
That should cover everything; good luck and let us know how it goes!
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