I have a similar situation. My Android (1st Gen Moto G, running Lineage OS, about 3 years old) shuts down once the battery level hits 15%. You can actually see

I have a similar situation. My Android (1st Gen Moto G, running Lineage OS, about 3 years old) shuts down once the battery level hits 15%. You can actually see it change from 15% to 1% for one brief moment before it shuts down. Sure, the battery is old, but this behavior is unlike the behavior of any other OS/device I've seen. I've seen some laptops with seriously messed up batteries and as far as I can remember, the OS reports a smooth discharge profile without steep drops and without and strange "surprises". I think Android is probably not taking battery health into account when it reports remaining capacity, but that is only a guess.