I have an 8 month old set of sub C sized 3200 mA 1.2 volt batteries rigged in 8.4 volt sets that I fully charged a month ago, then ran my train until it started to slow down. I forgot to immediately recharge them, and now they won’t take a charge.
Is there a way to save them?
Your charger is refusing to start because the pack appears to not exist because it’s voltage is 0. Take each cell and force about 3 volts into it for a few seconds. That will bring the cells above 0 volts. If you try to force the whole pack on all at once, you might reverse charge one or more cells. If that happens, the cell is dead meat. Then, the charger will start working.
So, I have to take the pack apart and force 3 volts into each battery? How do I do that? Most folks do not trust me with a light switch. 
Steve,
I might be able to save it.
I’ve done a couple of member’s who haven’t recharged like they are supposed to do.
Don’t take it apart yet.
I’ll call you tomorrow…
When I did it, I didn’t unwire the pack. I connected directly to the individual cells. A friendly helping hand is the best solution.
What Chemistry? I’ve never had this problem with NiCd or NiMH batteries in tools or cameras. Maybe my chargers don’t care?
Steve, check the output of your charger! That could be the problem. I do have two of TOC special charger which work for both NI & NiMH battarys. How ever I have wore out several sets of NiCads over the years.
Paul
P>S Must be all that snow!!
Was worried about one of my NiMH packs once. I’d packed up after a train show and forgot to unplug the battery from the receiver in the tender. Then, along about Thursday, I got around to… Ut oh. The charger didn’t even notice it was plugged in. Not knowing what else to do, I left it sit over night. In the morning, the charger’s light was green, and the pack has been fine.