My Black & Decker hand vacuum started slowing down sooner after about 2 years of very light use. It was always kept on its charging port. Being unfamiliar with these batteries I thought I should probably run it down all the way and charge it up from scratch. Well I ran it down alright, till it quit, but when I put it on the charger it just rapidly flashes all 3 of its charging lights at me without ever going into charging mode. I let it do that for up to an hour with no change. So now I don't know if the batteries are really killed or if this is some protection circuit function. B&D's website is no help, googling lithium-ion tells me these batteries don't like being fully discharged, that trying to bring them back involves expensive, specialized equipment and techniques. Ideas??