Both of these sit in the popular ~1,000Wh class, and on the spec sheet they look close. Independent bench testing is where they separate. Here is the measured picture, with every figure attributed to the lab that recorded it.
Real usable capacity
The Solar Lab measured the EcoFlow DELTA 3 Plus delivering 910 Wh of usable energy against its 1,024 Wh rating — 88.9%, the best in the 1kWh class. OutdoorGearLab measured the Anker SOLIX C1000 at 897 Wh usable of 1,056 Wh rated, or 85%. Close in absolute terms, but the DELTA 3 Plus returns a slightly higher share of what you paid for.
| Model | Rated Wh | Measured usable Wh | % delivered | Source |
|---|---|---|---|---|
| EcoFlow DELTA 3 Plus | 1,024 | 910 | 89% | The Solar Lab |
| Anker SOLIX C1000 | 1,056 | 897 | 85% | OutdoorGearLab |
Charging and UPS
Both recharge fast and both beat their own claims. The Solar Lab clocked the DELTA 3 Plus at 55 minutes on AC against a 56-minute claim, and OutdoorGearLab clocked the C1000 at 54 minutes against a 58-minute claim. Both held their loads as an uninterruptible supply in testing, with the DELTA 3 Plus measured at an 8ms switchover.
Where each one stumbles
The DELTA 3 Plus has a documented fan flaw. Under a 1,573W load The Solar Lab found the internals reached 138F while the fans would not spin up, which they called a glaring design flaw. T3 found the opposite symptom, with fans running constantly at idle. Its surge also measured only 2,600W against a 3,600W claim. The C1000’s main knock is noise: OutdoorGearLab called it one of the loudest units they tested at full load, and both Anker and OGL warn that its ultra-fast charging accelerates battery degradation.
Buy If / Avoid If
- You want the highest measured usable capacity in the 1kWh class — 910 Wh of 1,024 Wh, 89% (The Solar Lab).
- You need fast AC recharge — 55 minutes measured, beating the 56-minute claim (The Solar Lab).
- You want UPS-grade backup — an 8ms switchover measured in testing.
- You run sustained high loads — under 1,573W The Solar Lab found internals hit 138°F while the fans failed to spin up, a documented design flaw.
- You are relying on the 3,600W surge — it measured only 2,600W (The Solar Lab).
- Long-term fan reliability is a dealbreaker — evidence is contradictory (The Solar Lab saw fans not spinning under load; T3 saw them running constantly at idle).
- You want quiet-at-idle operation and a slightly larger 1,056 Wh pack.
- You need fast AC recharge — 54 minutes measured, beating the 58-minute claim (OutdoorGearLab).
- Expandability matters more to you than squeezing out the last few percent of usable capacity.
- Noise matters — OutdoorGearLab called it one of the loudest units they tested at full load.
- You would charge with ultra-fast mode habitually — both Anker and OutdoorGearLab warn it accelerates battery degradation.
- You want the highest usable-capacity ratio — it delivered 85% (897 Wh of 1,056 Wh, OutdoorGearLab), below the DELTA 3 Plus’s 89%.
The verdict
For efficiency and a slightly better real-world capacity, the DELTA 3 Plus edges it, if you can live with the fan behavior. If quiet-at-idle operation and expandability matter more, the C1000 is the safer pick, as long as you avoid habitual ultra-fast charging. Either way, size around the measured 85 to 89% usable figure, not the 1,024 or 1,056 Wh sticker. Full measured rankings are in our Honesty Index.
Full evidence page: Anker SOLIX C1000 Gen 2. See all in the product evidence library.
