I've repaired a few headphone wires; theyre usually thin copper wires covered with enamel insulation. Burn off the insulation with a blob of solder, or sand it off, and the solder will stick.
From an European view who has accustomed to imperial units, these discussions are so tiring. The metric vs imperial debates almost always come down to just personally preferring what you're familiar with. I've had the exact same feelings about imperial units as Americans express of metric. I really don't have a problem estimating what 10 cm or 1 kg or 1 kilometer or 2 degrees of Celsius difference in the weather is.
And the division issue is almost trivial in my view; you can just take 120 cm or 12 gram quantity. You don't magically lose the ability to divide things by other than 10 or 5 or 2 when using metric. Its not like decimal fractions disappear in imperial systems either. The metric system is there for making it easy to scale things between orders of magnitude and have sane conversions between units.
For seasonal grid-level storage, I wonder if simple compressed hydrogen storage (around 350 bar) is the most reasonable solution. AFAIK doesnt require any high-tech materials, avoids most embrittlement caused by LH2 and boil-off rates are reasonable.