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Comment by TeMPOraL | Hacker News Reader

A silly question then: why there are no AA/AAA rechargeable batteries that are Li-Ion/Li-Poly/whatever chemistry is used in smartphone batteries? Seems like a no-brainer to me: use the apparently better, more advanced, more energy-dense chemistry, but in a standard AA/AAA format. Pack whatever control electronics you need for safety too. Not only my remote controls would have half a decade of battery life, an iPhone could be powered off 2 such AAs, instead of 8-10 regular ones like other commenters here calculated.

Why isn't it done? Where's the catch?

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The catch is that Li-Ion rechargeable batteries have much higher self-discharge rate than alkaline AA/AAAs, so you could not use them in remote controls anyway.

For powering iPhones, you can buy a few 18650 with a type-C/lightning case from AliExpress, but most people will prefer just buying a powerbank.

> The catch is that Li-Ion rechargeable batteries have much higher self-discharge rate than alkaline AA/AAAs, so you could not use them in remote controls anyway.

How does that compare with NiMh, or whichever is the current standard chemistry for rechargeable AA/AAAs? I may be misguided here, but I generally avoid regular single-use AA/AAAs, as it feels like a complete waste of energy - even if properly disposed of, I don't imagine they get recharged by some factory and put back on the market, so all the embodied energy that went into making them is lost.

> For powering iPhones, you can buy a few 18650 with a type-C/lightning case from AliExpress, but most people will prefer just buying a powerbank.

At least some of the power banks I've disassembled in the past were just 18650s with a case, USB port and charging circuitry, so I can't blame people for buying it already pre-assembled.

NiMh is better but alkaline still lasts longer. For low drain devices like remotes where shelf life is a bigger concern than power draw, I’ve heard zinc is better still. These are often labeled “heavy duty.”

The Li chemistry produces much higher voltages and so would require step down circuitry to function as a direct replacement for AA/AAA. If you are talking about form factor, then there are a lot of similar size or smaller cells available.

I'm talking about having rechargeable AA/AAAs with higher power density, possibly using the same chemistry as in phones, laptops, drones, etc., so the industry could cut down on the amount of variation in sizes and connector types (which could possibly make the batteries somewhat cheaper thanks to less variation in manufacturing - though I suppose the price driver is still the chemistry).

What's the minimum voltage we could get without intervention? I'm not well-versed in batteries, but I do recall that a typical Li-Ion cell has 3.7V on output, which might be tricky to fit into one AA/AAA, but isn't that far from two AA/AAAs.

While there's no standard way for devices to accept multiple AA/AAAs, to a first approximation, a Li-Ion cell reformatted into a shape of two AAs with ~1-2mm "space" between them, would fit all my remotes and a third of my children's toys - so I could see a "Li-Ion double AA" working as a product, provided it could shed that 0.7V somewhere. The biggest problem would be devices accepting odd number of batteries.

There might be some market but anecdotally, AA/AAA as a widely accepted platform, and for that matter replaceable batteries in general, seem to be a thing of past.

I do have devices where the 2xAAs are in a column configuration.

Edit: Replaced remote with devices (it's a keyboard not a remote)

There are standard formats for cells in Lithium-based chemistries, but they are different sizes then the Ni-based ones because of the entirely different voltages. How (not) commonly they are used tells you something how much industry cares about avoiding many different sizes. (part of it is probably also that round cells are space-inefficient in devices that aren't tube-shaped - most common consumer use cases where the consumer handles individual cells are flashlights and vape devices, and some markets do have proprietary designs as de-facto standards)

Some manufacturers also make Li-Ion replacements for multi-AA devices, but thats then specific to manufacturer and device and the exact placement it expects.

They sell double-AA sized rechargeable batteries for XBox controllers. https://www.xbox.com/en-GB/accessories/batteries-chargers/pl...

This specific battery is unlikely to work for other devices because the controller has an extra connector, presumably to detect it and control charging (which happens over a USB cable). You'd at least need an XBox controller to charge it.

I think the issue is that li-ion isn't that much better than NiMH as to be worth it. It's also worth noting that there are already standard sized Li-ion batteries. 18650 batteries (so called because they are 18mm diameter by 650mm long) are the most common, but there are a bunch of other standard sizes. These are commonly used in things torches (flashlights) and headlamps.

Regular single-use alkaline AA batteries are more energy dense than comparable rechargeable lithium based ones (up to 3000mAh for a single AA vs 3200mAh for iPhone 14 Pro). They're also safer and have lower self-discharge.

That's 3000 mAh @1.5V vs. 3200mAh @...3.7V? That would give those alkaline AAs half of the energy density of a lithium one. And, that's single-use, which I'm not a fan of, because all the energy embodied in a heavy metal cylinder goes to waste.

High capacity rechargeable NiMH and lithium batteries are 1.2V.

The phone battery is bigger. For perspective, an 18650 battery is substantially bigger than a AA, but the best they can do is ~3500mAh. Iirc AA lithium batteries are barely more dense than alkaline or nickel, and are awkwardly high voltage so require a buck corcuit, further harming performance.

Lithium chemistry in a AA form factor, with integrated downconversion and even charging port and circuitry in each individual battery, are cheaply available on Amazon, eBay, newegg etc. Depending on how much you want to spend, they range from no-name companies lying about huge capacities, to real brands advertising (unfortunately in mWh!) genuinely useful capacities, and they are CHEAP. They handily beat Ni-mh batteries in pretty much every way; capacity, self discharge, useful voltage until they die (this actually has a downside in that device battery indicators can't tell that the batteries are running low), cycle lifetime, no annoying management like having to be careful when and how you charge your batteries etc.

You’d need a buck converter for discharging the battery, and they aren’t much better than NiMH batteries at it. So it’s cheaper to just buy Eneloops if you want AA/AAA batteries

I have some such AAA batteries. Not for the extra capacity - I'm not convinced they actually have any better capacity than the NiMH I was using before, but because they hold 1.5V for the duration of their charge, and for some reason my headphone can't cope with less than 1.5V.

There are such batteries, I saw them on Aliexpress. They are not cheap, though.

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