Archive for December 23rd, 2011

Ativa Cordless Phone Batteries

These were cheap-after-rebate phones with 2/3 AA NiCd cells that lasted nigh onto five years. We rarely talk on the phone and even more rarely use these, so they’re on the dreaded continuous trickle charge and low usage cycle that kills rechargeable batteries. Of course, they’ve been sitting there for five years…

The rebuild was no big deal, although I had to replace the original 360 mAh NiCd cells with 650 mAh NiMH cells (with tabs) because that’s what’s available nowadays. The trickle rate will be even lower relative to the capacity, of course, which may or may not be a Bad Thing.

The packs contained a simple fuse consisting of a thinned section of the usual nickel strap connecting two cells, covered with a fiberglass sleeve under the shrink overwrap. For lack of anything smarter, I harvested the fuse and soldered it in the new pack. although the risk of a catastrophic short seems fairly low:

NiCd pack with thin-wire fuse

NiCd pack with thin-wire fuse

The final result looks about as you’d expect, complete with obligatory Kapton tape wrap:

Ativa phone - rebuilt battery

Ativa phone - rebuilt battery

The old pack is kaput and new pack delivers pretty nearly its rated capacity at an arbitrary 550 mA discharge (which is, admittedly, a bit stiff for the old pack):

Ativa phone battery tests

Ativa phone battery tests

That takes care of one phone… the other one’s probably in the same condition, so I have enough cells to rebuild it, too.

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