If it was a different battery that is fine. That most likely means that the charging circuit is part of the PCB since 2.9 volts is not enough to charge a lion battery.
Welcome to your new home, stuart!
Sorry for the slow reply.
The charger has 4 terminals that correspond to T2, -, T1, and + on the battery housing. When I connect jumper cables between the cell and the + and - terminals, the charger shows a defective battery fault. I get the same fault when connecting to the T1 and T2 terminals also.
It seems like a pretty smart (but slow) charger. It is probably very safe when used as its meant to be used, but where is the fun in that? I think I will have to give up on using the charger. Oh well, I got a new 18650 and a way to keep the cats off of the counter. 
LOL! Nothing worse than turning you back for a second only to turn around and find someone has taken a bit out of your sandwich. Our cat usually points a paw at one of the kids whenever I inquire. Fortunately, he is too big to defy enough gravity to get as high as the table or the counters so I only have to worry when I break the house rules about eating in the living room.
Welcome to BLF, Stuart. It is here where the fun is just as important as the flashlights.
My Ryobis are Sanyo L
Ur18650sa N47A which is probably the date code google seems to say 1200 or 1300mah and 20 amp
If anyone wants to trade one or two of these batteries (unopened pack) for a new Redilast 3100, let me know. My Craftsman tools use the same batteries, and I wouldn’t mind a spare cell or two…
I plan on keeping the ones I have left. I believe the slickdeals thread contains a home depot inventory search. Maybe one in your area has some of these in stock.
If you are after high current cells I can also get some new ones for you. I just hate to see someone rip open a perfectly good battery pack when I have a legitimate use for these packs.
I can get just about any of the Sanyo, Samsung, Panasonic high current cells if that is what you are after…
Really I opened the one to see what was in there and if I could get it to work with the charger once it was out of the battery pack.
I am going to keep my remaining two in the battery packs to use in the motion detectors as cat deterrent.
Ok no worries. I thought you were going to also pull the others apart just for the cells, and didn’t want to see a perfectly good pack go to waste like that.