I got these for my electric guitar, which has a piezo bridge. I had previously tried conventional NiMh rechargables, but these tended to be over-sized and not fit properly in the battery compartment, meaning it did not close properly. I tried another cheap USB lithium rechargeable solution, but the voltage converter (I assume) introduced constant high-pitched noise that made it unusable for the guitar. I had almost given up, but found these. They are actually the correct size, and don't introduce noise! The piezo does not draw a lot of current so I have not ran the battery down to report on their capacity, but it has lasted a few months with no signs of stopping, and with everything else I am inclined to believe their claimed capacity. They cost more than other solutions, but it is worth it as the size and components are clearly better than competitors.