Building a replacement battery for the Wavetek/Fluke 7000/7001 DC volt reference

[TheSteve]

I recently acquired a Wavetek/Fluke 7001 DC reference. The battery in it was 21 years old so it was overdue for a replacement.

The factory battery is made out of 10 NiMH AA cells.
The battery in mine was made of 1200 mAh Varta industrial cells. Over the years they have made the packs out of higher capacity cells with the newest being over 2000 mAh in capacity.

Having had extensive experience with Sanyo(now Panasonic) industrial NiCad and NiMh cells I decided to use the Panasonic BK200AAP. This is a cell with a flat positive top(ideal for spot welding) with an average capacity of 2000 mAh and rated for 1900 mAh minimum.
Battery data here:
https://industrial.panasonic.com/ww/products/batteries/secondary-batteries/nickel-metal/models/BK200AAP
You will want to avoid higher capacity cells as to get that capacity the cells use thinner insulation between plates which makes them far less robust.
Before assembly verify the cells are all of equal charge and appear healthy.

The battery is held to the back panel of the reference with two bolts. Once they are removed the battery can be unplugged and removed through the side of the casing.
The battery has plastic caps over each end and the cells are glued together. There is also a temperature protection fuse that will open should the battery reach 70 degrees Celsius.
The plastic caps can be popped off and reused, if they don't want to move then you can apply some gentle heat from a hair dryer etc.
I took the new cells and glued them together in the same configuration as the original pack. As the mounting bolts go through the battery pack between the cells you can't have any glue in the middle of the pack. I used new tabs between the cells but reused the original thermal fuse and the battery lead tabs. They can be removed carefully from the original pack.
If you don't have access to a spot welder you can also buy AA cells with solderable tabs preinstalled, or if you're feeling very adventurous you can solder directly to the cells but this is never recommended and to be done with caution. Given the value of a 7000/7001 DC reference you want to use a properly built battery pack.
Once assembly is done verify the polarity at the connector - outside two wires(black) are negative and the inside two wires are positive(red).
It is also a good idea to add an updated date code to the battery pack.

Here are a few pictures of the build:

The original pack:


The new cells:


Cells spot welded - thinner tabs on the lower cells go to the thermal fuse which needs to be installed in this location to not interfere with the mounting bolts.


Cells spot welded second side:


Completed pack with updated date code:


New pack installed in the 7001:


A happy reference with his Fluke friends: