This...
Originally Posted by
gregf83
Best way to store Li-Ion: Charge them to 50% and check them in 6 months. Leaving them fully charged will work but degrades life a little faster. Heat and higher voltage will degrade the batteries faster.
Lenovo follows this guideline by offering an option to charge Li-Ion batteries in their laptops to around 50% and maintain the charge there while plugged in. I've used that setting for five years with my low end Lenovo and the original battery is still good. The only drawback is I have to manually choose this setting again anytime I unplug or reboot the laptop, otherwise it defaults to Windows settings and fully charges the battery before switching to trickle charge.
Generally I try to keep my old Nikon dSLR EN-EL4 Li-Ion batteries partially charged in storage, although approaching 12-15 years old they're pretty much at the end of service life even when not used heavily anymore. The more recent Nikon and off-brand Li-Ion batteries seem to last much longer.
NiMH batteries don't seem to be picky about charging. The manufacturing quality matters more than anything else. I've had some NiMH AA batteries that lasted for years and others that failed within a year, even when used, charged and stored similarly. I'm not sure brand name is a good indicator of quality either. Some of my longest running AA NiMH batteries were sold under their manufacturer names, recognizable only within the industry, while those relabeled as Duracell, Ray-O-Vac, etc., didn't last long.