I store some spare car/boat batteries in my garage, and you would think that batteries, in their plastic/insulated containers, should be fairly inert or impervious to odd discharge effects.
However, over years, I have noticed that if batteries are left on the bare floor of a garage, they will discharge over time. Something to do with gradual leakage via the plastic contacting ground (and maybe plus humidity) -- there is some conduction going on!
So instead, you have to store them on well-insulating platforms, say styrofoam or acrylic, and they will hold their charge far longer. But this is on the timescale of months -- I wonder how that relates to the timescale these researchers are investigating (and for often used batteries, I would imagine it matters less).
These little parasitic losses that are rarely studied...