How to Check Battery Health on a Used MacBook or iPhone

Why battery health matters more than anything else

On a used laptop or phone, the battery is the part most likely to have worn out. Screens, keyboards and logic boards usually last for years, but every lithium-ion battery loses capacity with each charge cycle. A device that looks perfect can still die by lunchtime if its battery is tired.

The good news is that Apple devices report battery condition in their own settings, so you can check it in under a minute — no apps or tools needed. Always do this before you pay, whether you buy from a store, a marketplace or a friend.

Checking an iPhone

Open Settings → Battery → Battery Health & Charging. You will see a Maximum Capacity percentage: how much charge the battery holds compared with when it was new.

• 90% or higher — excellent; the battery will feel close to new.
• 85–89% — good; normal for a phone that is one to two years old.
• 80–84% — acceptable, but expect noticeably shorter days and budget for a replacement.
• Below 80% — Apple considers the battery worn; iOS may show "Service" and slow the phone under heavy load.

Watch for "Unknown Part"

If the Battery Health screen says the battery is an unknown or non-genuine part, the battery was replaced with a third-party cell. It may work fine, but the capacity reading is no longer reliable and the phone will not show accurate health figures. Ask the seller who replaced it and when, and factor that into the price.

On recent iPhones you can also check Settings → General → About → Parts and Service History, which lists any replaced battery, screen or camera and whether the part is genuine.

Checking a MacBook

Click the Apple menu → System Settings → Battery, then the info button next to Battery Health. macOS shows a condition (Normal or Service Recommended) and, on recent versions, the maximum capacity percentage.

For the cycle count, hold Option and click the Apple menu → System Information → Power. Look for Cycle Count and Condition under Battery Information.

• Most MacBooks from 2010 onward are rated for 1,000 cycles before the battery is considered consumed.
• Under 300 cycles is light use; 300–700 is typical for a two-to-four-year-old machine.
• Above 800 cycles, plan for a battery replacement within the next year even if the condition still says Normal.

Numbers are not the whole story

A capacity reading tells you how much the battery holds, not how it behaves. If you can, use the device for ten minutes with brightness up: open a few apps, play a video, and watch whether the percentage drops unusually fast or the device shuts down unexpectedly.

Also look at the device from the side on a flat surface. A MacBook trackpad that clicks poorly or an iPhone screen that lifts at one edge can mean a swollen battery — a safety issue, not just a performance one. Do not buy a device with a swollen battery unless the price includes replacing it.

Quick checklist before you pay

Run through these on any used Apple device:

• Maximum capacity above 80% (ideally 85%+).
• No "Service" or "Service Recommended" warning.
• Battery listed as a genuine part, or replacement history explained.
• MacBook cycle count in line with the device’s age.
• No bulging case, lifted screen or stiff trackpad.
• Warranty in writing that covers the battery.