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The table under Technical Specifications confirms what I read elsewhere, that the non-rechargeable Lithium has the highest capacity. It may be the best choice for longest life inside an accordion.

That's been my experience for my guitars with built-in pre-amp - I use the 9v lithium batteries usually advertised for smoke alarms. My accordion takes two AA cells, and I've ordered lithium for that too.

I also have 2 Roland Street cubes, which run forever
on a handful of AA batterys, and have great sound and FX,
for the Solar Recharge power packs, as i said many are now
on the market tailored to Camping. These devices are basically
bricks of parallel LiPo cells with enough power/current/voltage to start your car
in an emergency.

A Roland Cube Street EX is on my wish list, I couldn't quite believe the specifications at what it manages on 8 x AA cells, but it gets good reviews and there is an option for a rechargeable lithium power pack. Meanwhile I just bought an old "Crate" busking amp, cheap and robust, but it uses a lead acid battery so it's heavy.

I have a "Jackery" brand powerbank, which (as you say) is aimed at camping. At 240Wh but only a couple of kilos it can run a 20W guitar amp all day.
One caution about 9-volt batteries. If stored or transported loose without protected terminals they can accidentally contact some conductive material (or worse, another battery) and could cause a fire. Those I buy come with protective plastic caps.

That is indeed a good warning!. I have printed protective plastic caps for my own 9 volt batteries. Better safe than sorry!