Battery health evaluation
Battery is the single biggest variable in used-phone pricing. The same iPhone 13 with 92% battery health vs 78% sells for $40+ less. This is the framework: how to read battery health on every major OEM, how it maps to grade tier, and when replacement is worth the cost.
The four battery readings that matter
- Maximum capacity (%): the most-cited number. 100% means the battery holds its design capacity; 80% means 80% of original. Below 80% Apple shows a "Service" notice; below 80% on Android is your own threshold.
- Cycle count: how many full charge-discharge cycles the battery has been through. Less direct than capacity but useful for cross-checking — 600+ cycles with 92% capacity is suspicious (likely calibration error).
- Peak performance capability: iOS only — flags batteries that throttle the CPU under load.
- Service indication: any OEM warning about battery health.
How to read battery health by platform
iPhone
Settings → Battery → Battery Health & Charging. Shows Maximum Capacity (%) and Peak Performance Capability. Cycle count is in Settings → Battery → Battery Health (iOS 17+). Beware: iPhone capacity reporting recalibrates after a few full charges, so a freshly-arrived phone may report higher than reality.
Samsung Galaxy
Use the Samsung Members app → Get Help → Diagnostics → Battery. Reports Battery Status (Good / Normal / Bad) and current capacity. The capacity readout is reliable on S22+ generations.
Google Pixel
Pixel doesn't show capacity natively. Use AccuBattery (Play Store) or *#*#4636#*#* hidden menu. AccuBattery needs 3–7 charge cycles to estimate capacity — not viable for a 5-minute test. For quick checks, use the cycle count from the dial code as a proxy.
OnePlus and other Android OEMs
Most rely on AccuBattery or similar third-party tools. Some models surface battery info in a Settings → About → Status submenu. OnePlus's *#808# diagnostic includes a battery test screen.
Battery thresholds by resale grade
| Battery health | Resale grade impact | Action |
|---|---|---|
| ≥ 90% | None — full grade | Sell as-is |
| 85–89% | ~$10–$20 reduction | Sell as-is, disclose |
| 80–84% | $30–$50 reduction | Sell as-is at next grade down, or replace |
| < 80% | Drops to "fair" grade | Replace before resale (almost always profitable) |
| < 70% | Often unsellable retail; parts only | Replace or part out |
When replacement is worth the cost
Battery replacement on most modern phones runs $25–$80 in parts plus 30–60 minutes of labor (or $50–$80 service fee at a repair shop). Resale-grade lift typically runs $40–$70 on iPhone 13+ and Galaxy S22+ when going from sub-80% to fresh battery. Net: battery replacement is profitable in nearly every case when the receiving battery health is below the platform's threshold.
Two exceptions:
- Sub-$200 devices. Older iPhone 11 / Galaxy S10 era — replacement labor exceeds the grade lift. Sell as-is at fair grade.
- iPhone with Apple's "Unknown Part" battery flag. Avoid aftermarket batteries here — the warning lives in Settings forever and signals to buyers that other components might also be aftermarket. Use Self Service Repair for OEM batteries on iPhone 12+.
Battery + cosmetic interactions
A phone with cosmetic Grade A but battery 78% is a Grade B device once tested. A phone with cosmetic Grade C but battery 95% is still Grade C — battery doesn't lift cosmetic grade. Buyers and platforms grade on the lower of the two scores, so a single weak component caps the grade.
Replacement strategy: lift battery first because it's cheap and the grade gain is reliable. Cosmetic refurb (back glass, frame work) rarely covers its own cost.
The disclosure rule
Always publish battery health on every listing. Sub-85% phones sold without battery disclosure are the most common refund cause on platforms with generous return policies. Disclosed honestly, the same phone sells for less but with no return — net positive.