iPod Touch 6 faulty battery indicator

I’ve had my iPod Touch 6 for about a year, and over the last few months the battery indicator has been wierd. For some reason iPods don’t have a numerical percentage indicator, so this is harder to document, but the battery indicator is very wrong in some cases. I usually charge my iPod overnight, and when I wake up it reads 100 percent (it displays the percent when plugged in but nowhere else). After this it loses battery life (according to the indicator) and soon displays the 20% remaining pop up (after about 1 hour of usage). However, after the 20% message I’ve found that I can use it much longer, at least another hour. The weirdest thing is that when I plug it in after using the battery as much as I dare past the 20% message, the battery indicator will fill up immediately and jump to almost half full from what seems to be almost gone, and when I unplug it, it will stay there. Also, if I leave it on the charger, it will charge extremely fast and then get stuck at 99% for a long time before finally displaying 100% Also In rare random cases the battery will display as low as it possibly can, even sometimes after I take it off the charger, then return to normal later I have so far adapted to this and began to assume that 99% means 60% and the 20% warning can be disregarded, but it is still annoying and I wonder why a numerical battery reading is not available for iPods. If anyone has an explanation for why this is happening, I’d love to hear it.