What symptoms were you seeing before you changed the battery?
How did the disassembly go? Was it straightforward? If you have never done anything like this before, then first of all, well done for having a go. Your next repair will take you half as long and will work out twice as well!
I would suspect you've probably disturbed a small ribbon-cable connector somewhere, or disconnected one and not reconnected it properly. These modern smartphones are assembled to unbelievably close tolerances in order to fit everything into the smallest casing possible. There is generally very little slack on the ribbon cables connecting sub-assemblies like batteries, cameras etc to the motherboard, and it's easy to accidentally yank one loose when reassembling. You are going to have to (carefully

) tear it apart again, and check each tiny connector to see that it is properly 'home'. The 'zero insertion force' connectors, which are basically just a row of exposed contact pads at the end of a ribbon cable usually have an insertion line across the cable, which gives an indication of how far they must be inserted for a proper connection. They also sometimes have a locking mechanism on the socket, at one edge of the face where the connector inserts. This will pull away from the socket when the cable is removed, and needs to be re-engaged after the cable is inserted. The type which use a small plastic plug with a number of pins corresponding to a socket on a board, are usually 'keyed' i.e. they have a (tiny) tongue somewhere that fits into a groove in the socket, or vice-versa.
My advice is to persist with it, but wait until you have an opportunity to do so with plenty of time to spare (if possible). Work in good light over a clean sheet of white paper to make it easier to spot small parts. Let us know how you get on...
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