test use of batteries with U-solder tags

[jerabaul29]

It looks like NKON has started to sell LSH20 with optional U-solder tags: https://ru.nkon.nl/saft-lsh-20-lithium-battery-3-6v.html . Consider testing it - this may allow to avoid bad contacts, and will allow 3 batteries in a standard RND box instead of 2 with the holders at present.