Successful TH720 battery re-build


Thanks to everyone that responded with info on the THS720, and my dead battery.
I made up a new pack, and took pictures, so anybody with the same problem can easily re-build theirs as well. By the way, the TH720 is the first Tek product I have ever had that DID NOT have the model number on the front, just TekScope, most odd.

In my case, I had both a dead battery, and dead wall-wart charger. I replaced the wall-wart with a nice 12VDC/1A linear unit, that worked great. The battery was much more of a problem.

The original design is a custom pack of 4 2600mA nicads in series with a very strange positive contact assembly. I chose to remake it using nicads (not NiMH as suggested) for many reasons, and the end result fits correctly, works and charges correctly and has more capacity than the original. A total win, in my opinion.

I used full-sized C 3000mAh nicads off ebay with welded tabs (very important!), they cost about $7 each. I attached them in a string, with minimal cell-to-cell spacing, and secured them together with a single turn of adhesive teflon tape (not the plumbers kind), this slides smoothly into the battery compartment.

I attached the weird positive contact ring and runner to the + end of the pack, and secured it in place with tape, so that the contact was correctly positioned and secure. once assembled, I marked it with a directional arrow (easy to put it in backwards!). it fit fine, and both charged and ran the unit, so I consider it a success. I will have a doc to send shortly (PDF) with pictures and info if anybody is interested.

all the best,
walter (walter2 -at-
sphere research corp.

Carsten Bormann

On 2020-08-28, at 20:27, walter shawlee <@walter2> wrote:

I will have a doc to send shortly (PDF) with pictures and info if anybody is interested.
Did anyone say “put it in the Tek wiki” yet today?

If anyone goes through with an 26650 (or 18650) Li-Ion hack, photos of that would be interesting to have in the wiki as well.

Grüße, Carsten