New unlocked iphone 5s (sprint original carrier) battery drains fast and takes longer to charge?

It's a brand new phone from EBAY. Everything looks good except battery.
it took about 2.5 hours to full charge, overnight it goes RED no SIM inserted and no usage just idle entire night, i upgraded IOS to 12.x still same issue. Please advice i like to retain this phone if battery issue is resolved otherwise return it.

You might as well return it. Trying to get it fixed will most likely cost you more than what the phone is worth.

If the phone is brand new, return it, so that the can exchange it for another new one.

More likely than not, you have a well cared for used phone that was factory reset. You feel it's new because you were told it was. New phones, even new ones 20 years ago, did not take two hours to charge. So this phone was either a returned damaged phone, or just plain used, either case, factory reset and very clean.

I have several old phones that don't have a scratch or rub spot on them. Just had been in a case from day one and never dropped.