Why battery health matters
A lithium-ion battery gradually loses capacity over its charge cycles. Its health is expressed as a percentage of its original capacity. Below 80%, a battery is generally considered worn: battery life drops noticeably and, on iPhone, performance may be limited to avoid unexpected shutdowns.
For a seller, knowing this figure means you can describe your device honestly. For someone buying refurbished, it is the first thing to check in a listing.
On iPhone
Open Settings > Battery > Battery Health (or Battery Health & Charging). The Maximum Capacity line shows the current capacity relative to that of a new battery. A message tells you if the battery is degraded and needs replacing.
On iPhone 15 and later models, Settings > General > About, in the Battery section, also shows the cycle count, the manufacture date and the date of first use.
If the screen mentions an unknown or non-genuine part, the battery was replaced outside Apple's network: mention this when you sell.
On Samsung Galaxy
Open the Samsung Members app, then Support (or Help) > Phone diagnostics > Battery status. The result tells you whether the battery is good, normal or weak. Depending on the model and the One UI version, the Settings > Battery and device care menu gives access to the same diagnostic.
On Google Pixel
On recent Pixel phones, Settings > Battery > Battery health shows an estimate of the remaining capacity. On older models, the Pixel Diagnostics app or Google support can run a test.
On other Android smartphones
Menus differ from brand to brand: search for “battery” or “battery health” in the settings search. Some brands build a diagnostic into their support app. Be wary of third-party apps that claim to measure the exact capacity: their results are estimates.
What it changes when selling or buying
- When selling: state the battery health if you are asked for it. A battery below 80% can lower the offer, because the buyback company will have to replace it.
- When buying refurbished: check the minimum capacity guaranteed by the seller and what happens if it is lower on arrival.
- Having the battery replaced by a repairer can be worth it before a sale if it costs less than the price difference on offer.