How long should I let it charge before replacing the battery?

This one was purchased with a bad battery, per the seller. I am not sure if it’s a 5 or 5.5, but I do not see the search function so I BELIEVE it is a 5th gen, and not a 5.5 if memory serves me right.

Anyway, as you can see the unit turned on despite the seller having a problem getting it to turn on themselves :-). However, I let it sit on the charger for ~20-30 minutes or so and it turned right off within a few seconds once I got it to my desk to plug into my computer to see if I needed to erase the iPod and replace the library.

How long should I give it off of a computer to charge before replacing the battery? This is a 30GB.