The trio of batteries I built for the Sony DSC-F505V two years ago faded away; that camera seems particularly hard on the batteries, perhaps because they’re two cells in parallel that don’t share well. Two of the three seem pretty well gone:
Back then, I bought 12 cells, built six into those batteries, and left six charged cells sitting in a bag. After rebuilding the two worst batteries with those new-old-stock cells, it seems they maintained a substantial fraction of their charge while resting in the cool and the dark:
However, the camera would regard them as discharged, because it infers charge state from voltage. Squinting at the curves, their condition after a few minutes is roughly equal to a new & freshly charged battery produces over on the right when it’s nearly discharged.
The other curves show the result after their first charge in two years: basically, full capacity. The fact that both pairs of curves come pretty close to overlaying means they’re still well matched.
The third cell isn’t up to their spec, but it’s close enough to not bother rebuilding right now: 1.2 vs 1.4 A·h.
The Kapton tape pull tabs work wonderfully well, as the rebuilt batteries fit the compartment rather more snugly than the un-hacked cases.
The Smell of Molten Projects in the Morning 