Preventative Battery Maintenance

Hope all is well , i see a lot of info about people changing out a cell or their entire hybrid battery once it fails , but im wondering if i can avoid waiting until any catastrophic failure to do so. Ive had a couple signs that my battery may be on its way out. For one , on more than one occasion i saw the battery level raise from 1 bar to almost full within seconds or vice versa

What im hoping is that i can test it , replace the damage cells now to avoid any further issues and get as much life as possible out of this battery without having to do a full replacement? I have some beginners experience with batterys , i built my own Lithium battery for my RV , i have a multimeter and i can deff test voltages without much issue. Would appreciate some guidance or maybe a good youtube video i can follow along with , thanks a lot

Adam