@x.h. unfortunately, batteries can die and the Alta's aren't an exception. I've had some that last for several days after several years of use and others that were short-lived right out of the box. If still under warranty, you can likely get a replacement, otherwise, accept you're using an out of warranty tracker and either charge more frequently like anytime you shower or drive, or you could replace the battery if comfortable soldering small electronics. Keep in mind it's a particularly small battery, perhaps the smallest of any of the Fitbits.
