Would it be possible to use standard 9v rechargeable cells? I’m sure the lifetime would be even less, but if a battery swap cost $10 and could be found at any corner drug store…

Id just personally go with replaceable parts. AA NiMHs are like $1 to $2 these days, and 6V 5Ah lead acid is like $20 (Lol, first hit on google is $4 from some no-name brand).

Replace the battery every few years and you're set. Rely upon mass production, standard part numbers and highly recyclable parts (lead acid wins at this).

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Lead Acid is particularly good at UPS style power usage patterns. It's very easy to perpetually trickle charge lead acid.

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If you're set on Li-ion, then use a standard 18650 cell, so you know that you'll always be able to buy a replacement. But given the attributes I see here, lead acid probably wins. So you have to replace a part every 3 years that costs $5 to $10, big whoop.

No, no, no! This is the post-apocalypse laptop! You can’t go off buying new batteries in your mad-max car. It’s gotta work from that solar panel!

A post-apocalyptic backyard garage could conceivably recycle a lead-acid battery, they're pretty simple.

As it happens, I've spent a lot of time over the last week talking to a guy in Romania who's trying to fix a sulfated lead-acid battery in his backyard garage. (I don't know if you've been to Romania, but the apocalypse happened 40 years ago there, so his available resources are kind of limited.) I think he's going to succeed, and may eventually progress to being able to recycle the lead into a new battery, but it's not going to be a weekend learning process or even a week-long one.

What kind of apocalypse happened in Romania 40 years ago?

I presume he's talking about the collapse of the Soviet Union, which caused a huge amount of upheaval in that area.

But I'm a poor student of modern history. Just throwing out a guess for now.

That sounds like the opposite of an apocalypse

Eventually it was good for Romania but IIRC, the initial collapse was very bad for the locals.

But again, I'd say that Eastern European modern history is my weakest subject by far. I probably should avoid talking about this subject lol.

Right, but I got the time interval wrong; it was only 30 years ago.

And in a Mad-Max future (lots of cars around, but not enough fuel), there will be plenty of Lead Acid batteries laying around to recycle.

I do consider it effectively an apocalyptic kind of battery design. It was invented in the 1800s, its chemistry is incredibly simple (Sulfuric Acid + Lead), and is very well studied.

i prefer the phrase "anti-apocalyptic." Because by designing an energy efficient laptop/phone, less lithium/capacitor resources are manufactured and everyone can have one, unlike that single coke bottle in that 80s movie, "The Gods Must Be Crazy" which will lead to one.

Did you consider the possibility of using a FPGA Lisp CPU? [0] I hope the supercapacitor idea works and you don't have a leakage issue.

[0] https://frank-buss.de/lispcpu/

FPGA soft core CPUs can't beat the same logic implemented in ASIC silicon in terms of static power consumption. The MCU at the core of this project has a very impressive uA/MHz specification that's difficult to achieve alone. I'm surprised to see it being much lower than even STM32L0 running off external SMPS

You can look into LFP (aka LiFePo4) cells, which have higher durability than lithium ion. Beware they have different chemistry so charging voltages differ from standard Li-poly or Li-ion (they are also safer, which is nice). I haven't looked at the data, but I suspect supercaps may not be optimized for very low leakage, and generally the energy density is not so good (though if you have access to energy harvesting I guess it may not matter!).