Sony NP-FM50 Battery Rebuild

With six new 18500 lithium cells in hand, I rebuilt the three weakest NP-FM50 packs.

The Sherline CNC mill setup for sawing around the midline:

Adjust the saw to cut along the seam, set X=0 at the surface, jog to about X+0.7 mm, jog the saw along the seam, then repeat for the other three sides. No real CNC involved, but it’s much easier than sawing or breaking through the seam by hand.

These two packs came with the camera:

The cells have only lot numbers, no manufacturer ID. Wikipedia sayeth Sony Fukushima started in 2000; perhaps these were early production units with no branding.

The center strap running the length of the pack didn’t seem long enough, because I mistakenly thought I’d straightened its end while unsoldering it. As it happens, the end was straight and secured to the PCB by structural solder:

Moral of the story: pay attention, dammit!

The other end of the center strap required a snippet of tin strip to reach the tabs:

Aligning the cells that way allowed me to just bend the other tabs over the PCB pads and solder them in place:

Then a strip of Kapton tape across the kerf holds the case together well enough to survive our gentle usage:

The battery packs require a brief stay in the charger to reset the PCB’s lockout circuitry, after which they work fine:

The two oldest batteries (OEM 2003 A and OEM 2003 B) have new identities to suit their new innards: 2019 E and 2019 F. The DOA eBay battery retains its 2019 D label after the rebuild, as there’s little room for confusion.

Admittedly, it’d be easier / cheaper / faster to buy third-party NP-FM50 packs directly from eBay or Amazon, but this way I know the cells aren’t complete crap and I get some Quality Shop Time™ out of the deal.

What’s not to like?