Every aftermarket iPhone battery listing claims a capacity. Most of those claims are optimistic. Some are fabricated. The difference between a battery that lasts two years and one that degrades to 70% capacity within six months almost never comes down to how it was installed — it comes down to the cell inside the casing.
The Problem with Capacity Claims
A genuine Apple iPhone 15 battery is rated at 3,349mAh. You'll find aftermarket iPhone 15 batteries listed at 3,500mAh, 3,600mAh, and occasionally higher. This should be immediately suspicious.
Battery capacity is determined by the physical size of the cell and the chemistry used. The iPhone 15's battery cavity has fixed dimensions. An aftermarket cell claiming significantly higher capacity in the same physical form factor is either using a thicker electrode stack (which risks bulging), misrepresenting its actual capacity, or both.
Independent capacity tests of aftermarket iPhone batteries routinely find the actual discharge capacity is 10–20% below the advertised figure. A battery claiming 3,500mAh frequently delivers 2,800–3,100mAh in practice.
What Determines Real Battery Quality
1. Cell grade
Grade A cells are first-run cells that pass full factory QC. Grade B cells narrowly failed Grade A QC, often due to slightly below-spec capacity or higher internal resistance. Grade C are cells that failed more significantly. Most premium aftermarket iPhone batteries use Grade A cells from manufacturers like ATL (Amperex Technology Limited) — the same supplier Apple uses for many iPhone models. Budget batteries use Grade B or C cells, which degrade faster.
2. BMS quality (Battery Management System)
Every iPhone battery includes a small circuit board that handles charging cut-off, over-discharge protection, and communicates with iOS for the battery health percentage reading. Cheap BMS boards misreport capacity to iOS, resulting in inflated battery health percentages that don't reflect real performance.
3. Connector compatibility
From iPhone 12 onwards, Apple implemented battery authentication that pairs the battery's serial number to the logic board. An aftermarket battery will display a "service" message and may show reduced health functionality. This is a software restriction, not a fault — worth explaining to customers upfront.
The Swelling Problem
Battery swelling is the failure mode that causes the most secondary damage. A swelling battery pushes against the display from the inside, cracking the OLED panel. Swelling happens for two reasons in aftermarket batteries: oversized cells and degraded cells that gas during discharge.
If a battery arrives with any visible inflation, do not install it. Return it. A swollen cell at the point of installation will only get worse.
iPhone Model-Specific Notes
iPhone 15 series: the batteries use a pull-tab adhesive system. Pull slowly at a low angle to avoid tearing. If the tab tears flush, use isopropyl alcohol to dissolve the remaining adhesive.
iPhone 12 and 13 series: two adhesive strips per battery. If strips snap, apply 90%+ isopropyl alcohol under the battery and wait 2 minutes before lifting.
iPhone X through 11: single adhesive strip. Take care with the surrounding flex cables.
iPhone 6 through 8 series: simplest battery design. The main risk is over-torquing the replacement battery connector.
Testing After Installation
- Charge to 100% and verify
- Check Battery Health in Settings → Battery → Battery Health and Charging
- Discharge test — run the screen at full brightness for 15 minutes and check that percentage drop is consistent with the rated capacity
- Check for swelling post-installation after 24 hours of use
Compatible iPhone Batteries at Buy2fix
We stock replacement batteries compatible with the full iPhone range, from iPhone 6 through to the iPhone 15 series. Browse our batteries collection — all batteries are Grade A cells with accurate capacity specifications.
Buy2fix technical team note: The single biggest quality indicator we've found is whether the supplier can tell you their cell manufacturer and grade. Transparency about the cell source correlates strongly with accurate capacity and longer service life.
