Aeiusny Portable Solar Generator 500W 288WH UPS Power Station Issues After 5 Years of Minimal Use

I'm having some trouble with my Aeiusny Portable Solar Generator 500W 288WH UPS Power Station. I've had it for about 5 years, but I've only used it 2 or 3 times. It was plugged in all the time to keep it charged. Now, it no longer shows how much it is charged, and when I turn it on, the flashlight just flashes on and off.

Two questions:

1. Is there a way to fix it?
2. What would be a good replacement for under $350?

Any advice or recommendations would be greatly appreciated!

Thanks!