If the charging light shows with the battery you should be good to go. If no light, likely the same fate as some of mine. They get dropped on the butt end, it often breaks the ribbon from the charging contacts.
Dremel with cutoff, just cut the shell along the grove around the bottom. This will expose the LOAD end of the cells.
You can charge the cells directly. Many will rejuvenate, some won't.
Got a sacrifice battery, cut off the bottom plate, then up the sides short of the top.
Cut across the back side (opposite the charge connections) and pry the case off (adhesives)
Pry the cells loose, you will expose the ribbon and you will see how the batteries are constructed.
"NO" you can't solder to the connection rivets (melts plastic first) but can unsolder the cells from the ribbon.
YEP, you can solder connections from any batteries like Li-Ion, wiring for power supply or even alkaline cell packs.
Full charge voltage should be 8.9 volts, 7.2 volt min under load. If that runs your RC truck, that should work fine.
Just use the truck charger for the Li-Ion pack though.
The top connections to the radio go directly to the cells. They make a 'shoe' you put on the battery in place of a radio and that has connections for a charger. Run into a battery with shorted cell, sometimes a high current charge will fix it. These have an internal 5 amp fuse, so keep that current below that, the fuse blows, the battery is history.
Sadly, I have miss placed that charging shoe or I would attach photos. A quick search, these may no longer be available. The one I got was Chinese junk anyway and broke a contact spring. I suppose an old dead radio could be butchered and make something similar.
Anyway, here is a battery with the bottom plate removed, I usually charge it with clips to the battery terminals:
73s
