An iPhone does not need a sim card for the battery to charge. Try turning the phone off and then back on again. If it still doesn't charge, it's possible there is something wrong with the battery.
The battery in my old iPhone 5 is about gone. I don't use it much any more, but some. I can charge it to 100% in the morning, then not use it at all and it's to 1% by late evening. You probably need a new battery.