Red / Green snake of death

Hi, my series 3 is pretty much new, only about 1 month old now, and I just bought it back in November on a sale from Walmart online. Brand new, out of the box, never used before until it got to me. About 2 days ago, I went to put it on after waking up only to realize it showed that it needed to be charged, so I did so. I let it charge for about 3 hours and upon my return, seeing that it still showed the red snake that it needed to be charged. I looked up how to fix this and it said to let it die completely to where the snake wouldn't show at all, did so today. I went to charge it up after letting this happen and the same thing is happening again. It starts off with a green snake for about 5 minutes or so, then alternates between the red and green snake every few seconds while "charging". I know 100% that it is not the outlet, or the charger since my sister's watch charges with no problem on my charger, so that cannot be the case. Is there anything else that it could be? Maybe the battery is bad or something, which I do not know how since it's only about a month old, not damaged, or dropped, nothing.

Thanks for any help!!!!