29c battery contacts


Hello HP fans.
I've rebuilt the battery pack in my 29c by cutting out the center bar and replacing the old cells with 1.2v nickel-metal hydrides (which I always charge outside of the calculator). This works fine except that sometimes I need to reposition the battery pack (by pushing it against it's springs slightly) to get it to power up. I did notice that on the original battery pack, the ends of the cells toward the springs were connected with a soldered on strip. Do I need to do something similar with my rebuilt pack to cure this glitch? Any other tricks that might be applicable?
All ideas appreciated.
Thanks very much, Hal.


The batteries should be strapped together on the end (you should not trust just the spring to connect the cells). Also there needs to be some slack in the strap so that the cells can move freely (they can't be glued together). I also clean the contacts in the calculator by applying a drop of DeOxit contact cleaner, gently polishing them with a wire brush wheel in a Dremel, wipe off the residue, and then use another light drop of DeOxit.

For stuborn machines (and all HP-19C and HP-10's) you may need to place a small wad of aluminium foil on each battery contact.


Thanks for your response David.
When I go to put the strap on, I'm assuming I can use a soldering pencil and a little silver solder, is this right? Any other tricks to soldering directly to a battery?
Thanks for your help, Hal


You really should have the strap spot welded on. Any battery store can do this (Batteries Plus, Batteries Etc). Heat from a soldering iron can easily damage batteries... but, if you are careful, ...

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