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My ZTE Quartz purchased on eBay from day one had problems with the battery. Very short runtime and sudden battery drop. Sometimes it fell from 50% to 0 within seconds.
I contacted the seller and he agreed to send another device (defective screen, battery ok). Before changing the battery, I connected to my phone and the same problem persisted (short duration and sudden discharge). There is the possibility of being the dock charge ?.
I now have two unused ZTE QUARTZ standing still.
https://youtu.be/b63l66TKYic (sudden discharge)https://us.v-cdn.net/6030075/uploads/528/QJLBB9NF9H9L.jpg