Should you find you are travelling without your device or need to leave it unused for multiple weeks or months, you'll want to ensure that it's charged to around 50 percent before turning it off. This will protect the battery cell from dying while left idle. The battery will still lose charge at a slow but steady rate, so after six months it will need charging back up to 50% once more. For more ways to get the best energy performance from your iPhone see our How to improve iPhone battery life guide, or if you're worried that the cell might be experiencing problems then read How to check iPhone battery health.