TENS machine. Used once, didn't like, perfectly good. It's nearly this model, but EM6300P not EM6300A: https://tensmachineuk.com/tens-and-muscle-stimulation/tens-machines/recharg...
NHS says: "TENS may be able to help reduce pain and muscle spasms caused by a wide range of conditions including: arthritis, period pain, pelvic pain caused by endometriosis, knee pain, sports injuries" (https://www.nhs.uk/conditions/transcutaneous-electrical-nerve-stimulation-t...).
TENS (transcutaneous electrical nerve stimulation) machine (New Marston OX3)
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