This round of Battery Myths debunks the idea that you should always let your battery drop to 0%. While this may have worked well for older batteries, it shortens the lifespan of modern Lithium-ion batteries. Plus, letting your phone shut down doesn’t necessarily mean that the battery has been fully drained. It may just not have enough energy to power everything needed.
The far better method to follow is to plug your phone in somewhere in between 30% and 40% charge. This will make your charging speed faster and will also preserve your battery’s life. For maximum battery health, keep your phone between 30% and 80% charged whenever possible.