NimH?
I've had some of mine refuse to take a full charge even when I know they're dead... I've brought em back with a verryyy slow charge, say 0.5A for a 5000, decharge, 1.5A, repeat... I haven't had one completely refuse a charge yet.
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Tiger I - Panzer II - Panzer III - Panzer IV - Chi Nu Kai - Panther G - KV-1b 756(r)
M4A3(76) Sherman - T-34/85 - M3 Grant - SECRET PROJECT