Steamdeck battery health dropped from 100% to 89%, is there a way to remedy this or is it just natural aging?

It happened very suddenly, I should add. Charge was on 96%, I was on desktop mode downloading mods for Stardew Valley and I checked my health and it was at 100%. I played on and off for a couple of hours and then my battery reached 13%. I put it on charge, left it until the light turned green and when I checked the health it said it was on 89% health. Have I done something wrong? Is this a potential glitch/issue? Or is it just inevitable? Thank you!