The OnePlus 15 ships with a 7,500 mAh silicon-carbon cell — one of the largest batteries we've put through our standardized smartphone test rig. Over 30 days of mixed use we measured screen-on time, idle drain, charge-cycle behavior, and thermal throttling on 120 W SuperVOOC.
Methodology
Each day followed a fixed pattern:
- Morning (9:00–12:00): 90 minutes Wi-Fi browsing + 30 minutes 5G video playback at 50% brightness
- Midday (12:00–14:00): Idle, screen off, push notifications active
- Afternoon (14:00–18:00): 60 minutes navigation (GPS + 5G) + 60 minutes light gaming (Genshin Impact, 60 fps cap)
- Evening (18:00–23:00): Mixed social + camera + reading
- Night: Charge from whatever level the phone hit by 23:00
Charging was always 120 W SuperVOOC unless noted. Ambient: 22–24 °C.
Screen-on time
| Week | Average SoT | Peak SoT | Days off charger > 24h |
|---|---|---|---|
| 1 | 9.1 h | 11.4 h | 3 |
| 2 | 9.4 h | 12.0 h | 4 |
| 3 | 8.9 h | 11.1 h | 2 |
| 4 | 9.2 h | 11.7 h | 3 |
Average across the month: 9.15 hours of screen-on time per charge cycle, with peaks above 12 hours on light-use days. For context, this is the highest SoT figure we've recorded on the standardized rig — about 40% above the iPhone 17 on the identical protocol.
Idle drain
Overnight drain (7 hours, screen off, Wi-Fi on) averaged 1.9% per night — 142 mAh in absolute terms. Silicon-carbon cells had early reputations for elevated standby drain; this generation shows none of it. Airplane-mode idle was under 0.5%/night.
Charging curve (120 W SuperVOOC)
| From → To | Time |
|---|---|
| 0 → 50% | 11 min |
| 0 → 80% | 21 min |
| 0 → 100% | 36 min |
The curve is front-loaded by design: the final 20% takes almost as long as the first 80% to protect the cell. Peak case temperature during charging was 39.4 °C at the 15-minute mark — warm, never alarming. Wireless charging at 50 W hit 100% in 58 minutes with slightly higher case temps (41 °C).
Degradation after 30 days
Using the OS's cycle-count and full-charge-capacity reporting plus our own discharge measurements, the cell showed ~1.2% capacity loss over 34 full-equivalent cycles. That's within the normal first-month break-in range for silicon-carbon chemistry, which front-loads its early-life fade (see why silicon-carbon changed the battery math). Extrapolating first-year loss to roughly 6–8% — in line with conventional cells.
Thermal behavior
Sustained gaming (60 min Genshin) settled at 42.1 °C peak case temperature with no battery-driven throttling; the SoC throttled GPU clocks ~9% at the 40-minute mark, which is silicon, not battery. Navigation + hotspot simultaneously — the classic road-trip killer — drained 11%/hour, meaning a full day of it still fits in one charge.
Verdict
The 7,500 mAh cell does exactly what the spec sheet promises: this is a genuine two-day phone under real mixed use, and a one-day phone under abuse. Fast charging is quick enough that the distinction rarely matters — 11 minutes at a café covers a full evening. The open question is year-two degradation, which no 30-day test can answer; we'll re-run the rig on this unit in 2027.
Spec sheet and score context: OnePlus 15 · iPhone 17 vs OnePlus 15 · all smartphones by battery.