This question came out of a lunchtime conversation with some colleagues, none of us who work in hardware or embedded: there was a period of time, up to the late 90s, where certain mobile computers and PDAs could be run off AAs for a long period of time, with sacrifices of I/O, display fidelity, and storage. Examples at the end.
Beyond size and aesthetics, is this possible today – or is this no longer possible?
(For example, do modern displays hoover up too much energy? Do 5G, Bluetooh and WiFi radios constantly suck power?)
Here were some examples of late-era portables that ran off AAs that we came up with:
- the Psion palmtop series used a couple of AAs, plus a coin cell battery for memory; and ran for a week [1]
– the Apple eMate, a Newton (ARM) in clamshell laptop form, which ran off 6 AA rechargable cells that could be swapped for off-the-shelf AAs, and ran for a week as well;
– similarly, the AlphaSmart Dana (Palm platform on 68k/ColdFire) and HP 200LX palmtops (PC-compatible) could be run off two AA batteries for around 30-50ish hours.
[1] https://news.ycombinator.com/item?id=40438434
You can do some rough back-of-the-envelope math for this. A typical smartphone might last about a day with a battery about 4500 mAh @ 3.7V nominal = about 16 Wh. That battery pack of 4 AAs is about 48 Wh, so it should run the phone for 3 days or so (with some losses). But depending on the phone, it may or may not be able to run off a standard USB outlet anymore (USB-A is usually limited to around 10W, some newer phones need ~18W to properly charge while on). But anyway that should give you an idea. With batteries and some electronics, you should be able to make a modern smartphone run off AAs. Here's a youtuber showing something like that: https://www.youtube.com/watch?v=-qObYrj1Foc&t=633s (or a DIY version: https://www.youtube.com/watch?v=TaoCPv0GTSg)
The question then is if you consider a "phone" a "computer". If not, probably you can find some Raspberry Pis, Beaglebones, etc. with a similarly low power draw. Or an Apple Watch, for that matter. From there it's just an issue of having enough AA batteries in series and some voltage converting electronics/USB ports to connect them to the smartphone.
There is nothing inherently impossible about this. Low-power electronics exist (in everything) these days. We just don't use AA batteries because li-ion is more energy dense (capacity per volume) than most AA chemistries, and if you're going to use li-ion anyway, a flat form factor is typically easier to carry around in a pocket than cylindrical cells.