Solar Steplight batteries dying after only four months?

I purchased seven solar steplights in March of 2023. I charged all of them prior to putting them into place along my deck steps. They get plenty of light, and were staying charged to 100% most of the time. However, in the last three weeks, four of the seven steplights' batteries have been going downhill. Three of those are completely dead and cannot be recharged using the USB method into the steplight back battery area. I removed a battery from one of the "good" steplights, and the steplight that was not responding began lighting up right away, just as you'd expect. This is why I believe the batteries are dead or dying in the four I'm having trouble with. What can be done here? I know I can buy new batteries, but should I have buy new batteries every four months? I think not. Please advise.