The shop either installed the wrong battery, or they were not an authorized Apple Service shop and they installed a "knock off" battery that will not perform correctly with your iPhone.
Take the phone back and have the shop install a genuine Apple battery. Unfortunately, if the shop is not authorized for Apple Service, they cannot obtain a genuine battery replacement part. In that case, your best bet would be to ask for your money back and then take the phone to an authorized Apple Service shop.
Use the link just below to find an authorized Apple Service shop:
Find Locations - Apple