High quality rechargeable battery teardown and repair

[electr_peter]

Some devices just shine with extreme quality once you take them in your hand. For example, take this battery case from small battery operated industrial instrument (~1988-1990 vintage).

It has very sturdy plastic case (no give or rattle). Battery attaches to main unit via massive brass (?) contacts and have locking mechanism. Once connected, it is rock solid. Two side contacts are for charging internal batteries.

Case is made from two plastic pieces, connected with two long screws. Screws have metal (!) (again, it seems like brass) caps to cover them from regular user - it is not supposed to come apart. Screws also have double grommets/soft washers to seal the unit. There is rubber seal around the main plastic lip.

Inside there is simple charging circuit, 2 AA sized batteries, paper for isolation and flex circuit for connections. All external connections are riveted (!) to flex circuit. Batteries have leaked slightly, but it would take much more to take out such sturdy construction.

As you can see, batteries are completely dead, but all is easily repairable. Can anyone give a hint what type of batteries are in that case? It looks like NiMh or NiCd cells, but I cannot discern. Any hints?

[kripton2035]

what is (should) be the voltage at the batteries pinouts ?
do you have any smart battery charger that could refresh them a little ?

[electr_peter]

what is (should) be the voltage at the batteries pinouts ?
do you have any smart battery charger that could refresh them a little ?

Batteries are completely dead. I have proper charging equipment, but these batteries are no more. They have ceased to be. They have expired and gone to meet their maker.

Circuit works from roughly 2.7-3V, 2.4 also should do. So nominal voltage should be in 1.2 ballpark. Thus, NiMh or NiCd are likely candidates.

[tautech]

For example, take this battery case from small battery operated industrial instrument (~1988-1990 vintage).

It looks like NiMh or NiCd cells, but I cannot discern. Any hints?

I have tried NiMh as replacements for NiCd with mixed results.
For high drain usage, I'd suggest you stay with NiCd's.
Maybe they're better these days, but heavy cyclic use killed NiMh for me.

[smjcuk]

Try some Sanyo Eneloops if you can - they are less painful than your average NiMh cell. Cycle many more times and don't discharge on the shelf.

However if you take a Sub-C eneloop apart, you'll be disappointed to find 4x AAA eneloops inside it!

[amyk]

1988~1990? Almost certainly NiCd.

[electr_peter]

1988~1990? Almost certainly NiCd.

I will order few spare NiCd cells then. High end Eneloop cells are expensive and have positive terminal sticking out, there is no way to solder them without spot soldering welding gun. mAh capacity is not critical, as current consumption is very low.

[SeanB]

Order tagged cells, as soldering to the positive terminal will damage the cell insulation and the overpressure vent. then it will leak caustic electrolyte all over the area.

Otherwise you can get the tags spot welded on by some local battery repackers, or somebody who has a small spot welder.

[tautech]

Otherwise you can get the tags spot welded on by some local battery repackers, or somebody who has a small spot welder.

I have successfully soldered tagged cells, small cells more so.
You must have an aggressive fluxed solder and tin the tags individually first.
IIRC it was with a Au alloy solder.
Hit them hot and hard for a quick tinning, load them with a little excess, line tags up and re-melt.

We all know cells get hot while charging, but you wouldn't want to heat them to this degree as localised heat at each end would be much hotter.

Maybe some abrasion to the tags might help tinning.

[smjcuk]

Abrasion works. Needle file and some multicore worked for me. I used to build battery packs for friends radio controlled cars. They were soldered from bare cells. Just keep the heat off by leaving them to cool between joints, tin them, wait for them to cool, jig them and solder the bars across. Never outgassed.

[SeanB]

12V car battery, carbon rod out of a cheap zinc carbon C or D cell ( any one, so long as it is not alkaline will do, you just want the rod), some heavy wire and the tag and you can make a quick and dirty spot welder that will do the weld in under 1 second with the sharpened rod applying pressure to the tab cell junction.  A puff of smoke, a sudden white glow and you are done with minimal heat into the cell end.