Battery life on a 13-inch laptop is governed by three factors: display power, CPU/SoC efficiency, and idle behavior. The MacBook Air M4 (IPS-LCD, M4 SoC) and the Dell XPS 13 (2025, OLED, Intel Lunar Lake) make different choices on the first two — making them an instructive head-to-head. We ran identical workloads on both machines for a full 8-hour workday, with continuous battery sampling every 60 seconds.
Setup
- Workload: Chrome with 12 active tabs (Gmail, Slack, GitHub, Notion, Figma, Linear, YouTube paused, Google Docs, Calendar, 3 reference articles), VS Code editing a small React/TypeScript project (live ESLint, no compile), Zoom in a 30-minute call at hour 3 and hour 6. ~80% browser-bound, ~15% editor, ~5% video conferencing.
- Brightness: both displays calibrated to 200 nits with a Klein K-10A colorimeter (auto-brightness disabled).
- Connectivity: Wi-Fi 6E on the same 6 GHz AP, no Bluetooth peripherals.
- Power profile: macOS "Automatic", Windows "Balanced".
- Ambient: 22 °C, no direct sunlight on screen.
- State: both machines at 100% with charger disconnected at workday start.
Hourly battery remaining
| Hour | MacBook Air M4 | XPS 13 (2025) |
|---|---|---|
| 1 | 92% | 88% |
| 2 | 84% | 76% |
| 3 | 76% | 64% |
| 4 | 67% | 52% |
| 5 | 59% | 40% |
| 6 | 50% | 28% |
| 7 | 41% | 16% |
| 8 | 33% | 3% |
After 8 hours: MacBook Air M4 had 33% battery remaining; XPS 13 had 3%. The Zoom call hours (3 and 6) account for the steeper drops on both machines — about 12% per hour during video calls versus 8% per hour during browser work.
Power draw breakdown
Using powermetrics on macOS and HWiNFO on Windows, average system power during the test:
- MacBook Air M4: 5.4 W idle, 8.1 W browser-bound, 12.7 W on Zoom
- XPS 13 (2025): 9.2 W idle, 13.6 W browser-bound, 18.4 W on Zoom
The XPS draws roughly 70% more average power across the same workload. Of that gap:
- Display: ~3.5 W (OLED at 200 nits draws more than IPS at 200 nits; OLED scales with content APL, but our test averaged ~50% APL).
- SoC: ~2.0 W (M4's 3 nm process and big.LITTLE architecture is more efficient at low-load than Intel Lunar Lake despite Intel closing the gap meaningfully).
- Memory + storage: ~1.5 W (LPDDR5X on both; the XPS's 32 GB config draws more than the M4's 16 GB).
Extrapolated runtime
- MacBook Air M4: ~12 hours of identical work to 0%
- XPS 13 (2025): ~8.3 hours of identical work to 0%
That matches Apple's marketed "18-hour" claim (which assumes lighter workload + lower brightness) and Dell's "20-hour" claim (best-case loop, OLED at 150 nits, no Zoom). Both manufacturers' claims are honest for their best-case scenarios; real-world is what we measured.
What's actually killing the XPS battery
The XPS 13's OLED panel is the single biggest culprit — about 40% more display-only power at the same calibrated brightness. The CPU efficiency gap matters less in this workload (mostly idle-to-light browser load) than the display difference. If you ordered the XPS with the non-OLED FHD+ option, the battery gap shrinks to roughly 60% — still behind the M4, but more in line with x86 expectations.
What this means for the buying decision
- You need 8+ hours unplugged regularly → MacBook Air M4.
- You want OLED and accept the battery trade → XPS 13 OLED.
- You want OLED + battery → XPS 13 with the FHD+ IPS option, or wait for the OLED-LTPO variants that are rumored for late 2026.
See the full XPS 13 vs MacBook Air comparison for performance, build, keyboard, and port differences, or our best laptops under $1,000 guide for the broader category.