Aging (increased series resistance) is gradual. Open cells cause a sudden loss proportionately, like a drop to 1/2 or 2/3 capacity of what was expected. Shorted cells can cause those particular sudden onset symptoms. Lithiums can develop high resistance shorts (hundreds to thousands of ohms) that cause minimal heating but cause state of charge to drift out of balance. So after some time one section has low state of charge relative to other sections. It discharges first, and the other sections in series that are almost fully charged recharge first then stop the charge to avoid getting overcharged. The continued leakage in one section eventually gets its voltage so low that charging is inhibited altogether for safety reasons. Older battery pack designs have no cell equalization provisions and newer ones have limited ability to compensate for internal shorts. If you carefully open and measure cell group voltages in such a battery, one section will be really low compared with the others. Even if you were to surgically recharge just the low state of charge group, it would self discharge itself again requiring manual intervention. No cure except by recelling.