iPhone batteries degrade chemically over every charge cycle, and Apple's iOS provides tools to monitor their condition. The most direct check is in Settings > Battery > Battery Health, where users see either Normal or Significantly Degraded. On iPhone 15 and newer, the total cycle count is displayed; older models are designed to reach 80 percent capacity at 500 cycles, while newer models target 1,000 cycles.
Beyond the health menu, several warning signs indicate a battery may need servicing. These include needing a power bank to get through the day, rapid percentage drops, unexpected shutdowns when the battery is well above single digits, and sluggish performance during heavy tasks like gaming or 4K video streaming. The device may also heat up quickly when unplugged or barely in use. A bulging battery is a safety hazard and warrants immediately stopping use and contacting Apple Support.
Replacement pricing varies by model, from $69 for an iPhone 6s battery to $129 for an iPhone 18 Pro Max. For those with an active AppleCare subscription, there is no service fee if the battery has dropped below 80 percent. The source notes that recognizing these signs early can prevent day-to-day issues and sudden shutdowns, making the built-in battery health tools a useful first step. There is only one source for this information, so no independent comparison is available.