Battery won't charge after replacement installed

Planned to replace my ipod's screen since the touch digitizer wasnt working and it had cracked so i figured i should replace the battery also since i was having to charge it almost every night. ipod touch 2nd gen 8gb, not jailbroken, a referb, not too old.

TL;DR(as its a bit long), soldered in a replacement battery, charged up perfectly fine once, normal lifespan... but now that it has died it wont take a charge.

bought parts off amazon, took it apart, removed the old battery after heating the soldering points and soldered in the new one, from below (solder between the ribbon cable connections and the points on the circuit board). worth noting that some of my research on this repair pointed to the notion that it was a better idea to do it from above, but i had my dad help me with the soldering as he knows a fair bit about electronic hardware and he said it was ok to do it from below. reattached everything, cleaned some fingerprints off the LCD with isopropyl alcohol(carefully), put in new screen/digitizer.

powered it on fine, initially it said it was at low battery. plugged it into my computer, put lots of new music on it and let it charge overnight, key element here is that it did charge up from 20%-ish, "20% battery remaining" warning message territory, to 100% the first time. problems began after i killed the battery for the first time. life span seemed pretty normal. ipods ive had before definitely experienced loss of capacity due to charging all the time/charging up from half power, things like that so i usually am not so quick to charge my ipod up unless it is dead, to keep my battery 'fit', so to speak. once the battery died i tried to turn it on a few times to make sure it was dead (sometimes it can turn on again after it dies), and plugged it in the wall socket to charge (wall USB socket for my phone, used with ipod cable, this is definitely strong enough to charge my ipod as i have been using it for this for a long time). worked normally at first displaying the one red sliver of battery and the lightning bolt indicating it is charging, but after charging overnight it hadnt turned on but still remained at the same red battery sliver screen. the ipod doesnt turn on but does respond to being plugged in and is not detectable by my computer/itunes/anything that i know of.

tried plugging it in again a few times. earlier after i started experiencing these problems, when i would attempt to power it on while it wasnt connected to anything, i would get the red battery sliver with the electrical plug icon pointing to the lightning bolt, prompting you to plug it in. however now it will not display that screen and also the low battery image will immediately disappear off the screen if i unplug it while it is displayed, instead of remaining for a few seconds and changing to the electrical plug/lightning bolt low battery image, i think, indicating some residual power left that has since depleted from displaying the plug image as i tried to power it on a few times. probably useless information and this might be a dumb assumption, i really dont know : /

any help would be very, very greatly appreciated, or any assumptions as to the componet at fault, what caused the problem (bad soldering job? repeated attempts to power on?) and how fixable it is, or whether part(s) must be replaced. anything you feel might be helpful.

please help!!