Free battery health calculator

Some phones show it directly: newer Pixels under Settings, Battery, Battery health, and many Samsung phones in Samsung Members diagnostics. Otherwise a battery app can estimate it from how much charge goes in during full charges. Lithie measures it from your own charges and labels every figure.

Above 90% is in good shape. Between 80% and 90% is normal wear after a year or two. Below 80% is where most phone makers consider a battery worn, and you will notice shorter battery life.

Design capacity is what the battery was built to hold, for example 5000 mAh. Full-charge capacity is what it actually holds now. Health is the second divided by the first.

Lost capacity does not come back, but you can slow further wear by avoiding heat and not keeping the phone at 100% for long. A charge limit around 80% to 90% helps, which some phones and Lithie offer.