|I think you should try the hot melt, you have nothing to lose. Put a dab of glue on each side of the battery where the tabs stick up (see your pic). That will hold the battery in place. Then come up with a way of connecting the + . If you lost the clip, paul1149's idea of using a paperclip might work. Bend it, cut it, twist it, whatever you have to do. If you can wedge it in place & bend it so that it keeps pressure on the top of the battery, it should work. The only other alternative is to de-solder the old battery holder & solder a new one in place. There's only 2 solder points. Of course, it means you will have to completely disassemble everything & remove the motherboard to be able to work on it.|
Also, do you understand that the battery isn't absolutely necessary? All it does is retain the BIOS settings in memory when power is disrupted to the tower. Obviously it would be inconvenient not to have a battery, but as long as you never unplug the tower or switch off the power strip, the BIOS settings will be retained.