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In two cases, I experienced that a device does not work, or does not work correctly, with rechargable batteries, while one-way batteries do the job. Can that be, and if so, why?

The two experiences where:

A radio-controlled wall clock designed for I think one AA battery. The initialization failed -- no matter how long I waited, it always did a round-trip to 12:00, then ran to the correct time, then returned to 0, and remained there forever.

A bathroom scale designed to use four AA batteries. It simply does not work, as if there were no power source at all.

The batteries that worked in both cases were plain vanilla AA batteries. The recharchables I tried were of the various kinds I have in my household, for example, Ansmann2100 mAh NiMH AAs.

The charger I use is a Cellcon "Super 1 Hour Easy Bi-MH/Ni-Cd Battery Charger Model C-250". It has a nice LCD display indicating charging status, and progress, and I always waited until it say "Charged" for all four AAs I insert.

Of course, I tried brand-new, then older, but verified-to-work rechargeable AAs, but the result was always the same.

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    \$\begingroup\$ Well get this then I have a led lantern that takes three AA and most of my rechargeable NiMH (Tenergy,Radioshack,others) Do Not work in it. But Energizer NiMH and Enaloop NiMH Do work just fine even if they are all the same voltages. So I think it has a little more to do with internal circuitry. \$\endgroup\$
    – JAY
    Commented Sep 23, 2022 at 2:49
  • \$\begingroup\$ Yeah meanwhile I can ack too that it is not solely the voltage on the label, but also the brand. Maybe there are minor differences in the voltage, I have not measured so there might be a small but relevant V difference between brands \$\endgroup\$
    – TheBlastOne
    Commented Oct 7, 2022 at 13:18

3 Answers 3

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An alkaline cell has a nominal voltage of 1.5 V when new.

A NiMH cell has a nominal voltage of 1.2 V when charged.

Your equipment might be expecting a higher voltage than the NiMH can supply.

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NiMH rechargeables have a lower voltage (1.2-1.3V) than a new alkaline or whatever normal battery (1.5V) from the start, see e.g. https://de.wikipedia.org/wiki/Nickel-Metallhydrid-Akkumulator

Alkaline batteries' voltage decreases during use and may reach 1.2V after some time, too. So, a fully-charged NiMH may look to a device like a half-or-more discharged alkaline.

Some devices are ok with running off 1.2V (which drops even more as the battery discharges) instead of 1.5V, and some just don't.

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AA is kind of small for conversion, but there are rechargeable conversions in 9V batteries. Of course they have to include a step-up converter to reach 9V from a lower input voltage.

https://www.youtube.com/watch?v=NVKh-PCSj3E

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