Why are rechargeable AA/AAA batteries 1.2v not 1.5?

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Why are rechargeable AA/AAA batteries 1.2v not 1.5?

Post by Higgy » Sun Feb 21, 2021 2:51 pm

This has been going round my brain for years, and as we are doing a household inventory of batteries I saw it again and reminded me why are rechargeable batteries not 1.5v?

I guess there is probably a 'oh, I see' reason. But surely they can make them any voltage.

It just seems like your short-changed before you start.
(I think this all stems from back in the day when my GameGear used to run out so damn quick. In the end I used a 7.2v radio control car battery as per an Atari Lynx owning friend. Just a shame back then those 7.2v batteries took all day to charge!)

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Re: Why are rechargeable AA/AAA batteries 1.2v not 1.5?

Post by czietz » Sun Feb 21, 2021 3:14 pm

Well, the voltage is given by the way battery chemistry works.

However, it's only half-true that alkaline (non-rechargeable) batteries have 1.5 V. They do so when new, but when using them, the voltage quickly decreases. In contrast, with a NiMH rechargeable battery, the voltage stays more or less constant at 1.2 V. This means that if you have a device which ceases to operate at 1.1 V (cutoff voltage), you're in fact better off with a rechargeable battery:
Unbenannt.PNG (87.88 KiB) Viewed 273 times
Source: https://cdn.shopify.com/s/files/1/1356/ ... 1595713938

More discharge curves here: https://www.powerstream.com/AA-tests.htm

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Re: Why are rechargeable AA/AAA batteries 1.2v not 1.5?

Post by exxos » Sun Feb 21, 2021 4:11 pm

Look up the natural voltages of the elements zinc and carbon for starters..
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Re: Why are rechargeable AA/AAA batteries 1.2v not 1.5?

Post by tzok » Sun Feb 21, 2021 8:41 pm

Terms "battery" and "cell" are often used interchangeably, however the cell is a single unit, which voltage is denominated by chemistry used inside. While a battery may be build from one or more cells (to be technically precise from two or more cells), and its voltage is a multiple of a single cell voltage. Most consumer batteries are in fact single cells, like D (R20), C (R14), AA (R6), AAA (R3), but there are some multi-cell batteries too, like 6LR61 (alkaline 9V "block" type battery, which has inside 6 cylindrical cells type LR61), 6F22 (zinc-carbon 9V "block" type, build of 6x flat F22 cells) or now obsolete 4.5V "block" battery 3R12 (which had 3x R12/B-type cells inside).

So no, the battery can't have any voltage.

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Re: Why are rechargeable AA/AAA batteries 1.2v not 1.5?

Post by Atarian Computing » Mon Feb 22, 2021 10:44 am

Also, 1.2v is the nominal voltage of the cell. When you charge it up it can get to 1.4-1.45V.

Same with 3.3V LifePO4 cells. 3.3V is nominal while fully charged it is 3.65V.

"Regular" lithium cells have a nominal voltage of 3.7V and fully charged 4.2V.

12V car batteries are no different. If a car's battery actually measured 12V when the car was off, the battery is toast and would not start. That's the nominal voltage. It should read over 14V while car is on (charging).

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