Sony InfoLithium Battery Autopsy & Observations
Used on Sony Handycams old and new, the InfoLithium L series camcorder batteries have proven to be pretty resilient and can usually come back to life quite easily after sitting disused and discharged for many years--even decades. The smaller, newer InfoLithium M series batteries seem to be a bit more hit or miss.
Oddly, the small capacity M series batteries seem to be a bit more robust than their larger capacity counterparts. I tried charging and using multiple Sony QM-71D batteries that showed a full charge on their built in charge indicators, but they'd die almost immediately. Attempts to fully discharge and recharge them were unsuccessful, since they always behave like they're at 100% charge, until you actually go to use them.