[Ryobi battery cutting out early]

Just to clarify further. It's a Ryobi One+ battery and it has worked just fine for the last 4 years. Moderate to low usage.

[Ryobi battery cutting out early]

I have a 4yo 5Ah battery. It now charges fine but stops delivering power once the first bar is extinguished. I can still see 3 power bars and it doesn't tale long to recharge. So, there is still power in the battery but not being delivered to the devices. 

Suggestions on a fix, please.