iPhone battery health: how to check it and what each value means

Battery health (labelled in iOS as Maximum Capacity) is a percentage that tells you how much energy the battery can still hold compared to when it was brand new. A battery at 100% capacity holds a full charge, while a battery at 85% holds roughly a seventh less — meaning the phone needs charging a bit sooner.

It's a soft metric: iOS calculates it from charging history, cycle count and the cell's behaviour under load. That's why the value sometimes jumps by a few percent, and after extended use it may adjust slightly up or down following recalibration. This doesn't mean anything is wrong with the phone.

A lithium-ion battery always ages — through use and simply over time. Apple states that the iPhone 14 and earlier retain roughly 80% capacity after 500 full charge cycles, while the iPhone 15 and newer retain it after 1,000 cycles. One cycle isn't a single charge: it's the consumption of 100% of capacity, which can happen in parts over several days.

The process is the same for the iPhone 8 and later (older models don't display this value).

A rough interpretation of the values you'll see in iOS. This applies to normal use without extreme temperatures.

We measure battery capacity for every unit during the thorough initial technical inspection, and it's one of the criteria we use to grade the phone's condition.

• Unopened — a never-activated phone in a sealed box, 100% capacity.
• Like new — capacity typically 92–100 %.
• Grade A and A- — capacity typically 90% and above.
• Grade B and C — capacity 86–100%.

The 86% threshold applies across our entire range: we won't sell a phone with lower capacity until it gets a new battery. You'll find the exact measured value in the item's description, and you can verify it again in Settings right after switching the phone on.

If the battery health doesn't match the description after you receive the phone, you have 30 days to return it without giving a reason, plus a 2-year warranty on the whole phone.

iOS can display several different messages, and each means something different:

Service Recommended / Battery Service — capacity has dropped enough (usually below 80%) or the cell is behaving abnormally, so Apple recommends a replacement. The phone keeps working, just expect shorter battery life.

Important Battery Message: Unable to verify this is a genuine Apple battery — the phone has a non-original or unauthorised replacement battery. iOS then often doesn't show the capacity percentage at all. For a phone from a classified ad, this is a warning sign — you don't know what's inside.

This iPhone battery is not able to provide the necessary peak power — the battery can't supply enough current, so iOS reduces the processor's clock speed to prevent random shutdowns. This can be turned off in Performance Options, but the recommended route is a battery replacement.

None of these messages should appear on any phone we sell — a phone with a non-original or flagged battery won't pass our initial inspection.

A very common misconception is assuming that a phone with 88% capacity will last 12% less time than a new one. In reality, battery life is affected by far more factors than capacity alone:

• Screen brightness — the display is the biggest power consumer in the phone. Keeping brightness at maximum permanently uses more than 10% of battery capacity.
• 5G in areas with weak signal — the modem constantly searches for a network. Switching to 4G in such a location extends battery life much more noticeably than a battery replacement.
• Background apps — social media and navigation apps with constant location tracking can drain the phone even without you doing anything.
• Temperature — in cold weather the battery temporarily loses capacity, while in heat above 35°C it suffers permanent damage.
• The model's battery size — the iPhone 15 Pro Max has a physically almost double-sized battery compared to the iPhone 13 mini. A model at 86% can last longer than a smaller model at 100%.

In other words: if battery life matters to you, look at the specific model's battery size (Apple states it in hours of video playback), not just the health percentage. You'll find an overview of all model capacities in our technical iPhone overview.

Battery health is the easiest way to spot a phone that isn't in the condition the ad claims.

You can't get lost capacity back, but you can significantly slow further ageing:

1. Keep the charge between 20 and 80%; deep discharging to zero harms the battery the most.
2. Leave Optimised Battery Charging turned on, or on the iPhone 15 and newer, set the charge limit to 80%.
3. Don't charge the phone in the heat — a car in the sun or charging under a pillow is the worst combination for the battery.
4. Remove a thick case during fast charging, as heat is the cell's main enemy.
5. If you're not using the phone for a long period, store it charged to roughly half.

A detailed guide including iOS settings can be found in the article how to extend your iPhone's battery life.

You can check battery health in ten seconds via Settings → Battery → Battery Health & Charging. A value above 86% means a fully usable phone; below 80% it's time for a new battery. However, health isn't the same as battery life — two different models with the same percentage can have battery life that differs by half.

If you'd rather not worry about battery health at all, choose a phone with a verified battery: every pre-owned iPhone in our range has a measured capacity of 86–100%, a 2-year warranty and delivery within 2 working days, or free in-person collection at selected iLoveServis stores.