I recently picked up a HP 3457a 6.5/7.5 digit DMM! It is an old workhorse, fairly common in the 80s and 90s.

My 3457a seems to be working well, but I am a bit skeptical about the sram backup battery, which appears to be an original – it might be 30 years old.

Since I intend to send this out for calibration, it is worth replacing ahead of time. If this battery fails, I’ll have to spend more to get it calibrated/adjusted again anyway.

A bit of surgery with my Weller WX-1, with a 3.5mm jack inserted in tha back to make it float, allowed me to desolder the existing battery while the meter was running. It is very important to use an isolated soldering iron – otherwise you will short out the battery as you desolder it! I cut the battery off before de-soldering the pins.

I replaced it with a Panasonic BR-2/3AE5SPN, a primary long life 3V lithium cell, 2/3 A size, with PCB mount pins (with the right spacing!) already welded on.

The 3457a rebooted several times during the process which was extremely unnerving, but it seemed to work out ok.