EcoFlow Delta Pro battery review: maximum solar power for an uncertain world

It’s hard to imagine, but there could soon come a time when a 100-pound battery on wheels that costs $3,699 is something you’ll want or even need.

Maybe it’s because you want to take out some insurance in the form of emergency backup power now that the public grid is increasingly under siege by heatwaves, fires, and floods. Or maybe, like me, you just want to take advantage of your employer’s new work-from-home policy to disappear into the forest for weeks at a time with a laptop, Starlink RV, Super73-ZX e-bike, and all the latest gadgets that define modernity.

Either way, you’ll need a very powerful battery, and one that’s flexible enough to be refueled by whatever means is available. In other words, something like the Delta Pro from EcoFlow.

The Delta Pro is a suitcase-sized battery designed to handle the unexpected. It’s relatively portable, loaded with DC and high-wattage AC outputs, and can be charged in half-a-dozen ways including solar panels and from thousands of level 2 EV charging stations.

Not only did a 3.6kWh Delta Pro and 400W EcoFlow solar panel keep all my family of five’s gear charged for three weeks without dropping below 55 percent, but this big-ass solar generator also proved capable of charging an RV and an entire house without even flinching.

I’ve been covering EcoFlow since the company launched its first product in 2017. In that time, it has gone from making standalone batteries to creating an entire ecosystem of products that build upon one another as your needs evolve. Sonos customers will immediately recognize the approach: you start with a single speaker, then a second for real stereo separation, then a Sonos soundbar to create a home theater, and later a subwoofer to round out the 5.1 sound. At this point, you’re so locked in you’re unlikely to buy anything else.

With EcoFlow, you buy one of its flagship 3600Wh Delta Pro batteries, then an EcoFlow expansion battery or two to boost capacity to 10.8kWh, and then some EcoFlow solar panels to keep it all charged in an environmentally friendly way. You find you’re not using your $10,000 setup all the time so you fit an EcoFlow smart home panel into your electricity box so that the entire house can still be powered during a temporary blackout, and then add an EcoFlow dual-fuel generator for serious emergencies to keep everything powered for as long as you feed it diesel or propane. Or maybe take all that gear off-grid to augment the performance of EcoFlow’s turnkey Power Kits installed in a remote cabin or RV. Then kick back with a portable EcoFlow AC unit in comfort and watch the fossil fuel-obsessed world burn.

I reviewed a European model of the Delta Pro, which differs only slightly from the US version. The EU model has four 230V/16A AC outlets, whereas the US model has four standard 120V/20A outlets and one 120V/30A. Both models produce up to 3600 watts (with a 7200W surge) which is enough to power just about any major or minor household appliance you throw at it.

The Delta Pro is fitted with a new generation lithium iron phosphate (LFP or LiFePO4) battery which has several advantages over typical lithium-ion batteries. These include faster charge times, longer life, lighter weight, and improved safety. EcoFlow says the Delta Pro will still be at 80 percent capacity after 3,500 cycles, which would take almost 10 years if you were to charge and deplete it every day. By comparison, an iPhone’s lithium-ion battery hits the 80 percent mark after just 500 cycles.

Ecoflow says the Delta Pro’s 1.8-hour charge time is the “world’s fastest.” It achieves this impressive figure by combining multiple charging methods for a maximum input of 6500W. The Delta Pro can be charged in six different ways.

I only tested three of the Delta Pro’s six charging methods: regular AC input via shore power while parked at an RV site (fast at 2900W max), via the 400W portable solar panel I packed (reasonably quick in full sun), and from my van’s 12v socket while driving (slow, but better than nothing). My review unit didn’t come with the optional Type 1 adapter that allows it to charge at up to 3400W while parked at an EV station. The other two charging methods are proprietary EcoFlow solutions I also couldn’t test: the EcoFlow Smart Home Panel (3400W), which turns the Delta Pro into a short-term battery backup for your home, and the EcoFlow Smart Generator, which will charge the battery at 1700W using diesel or propane fuels.

For this review, I brought along a large EcoFlow 400W solar panel. The Delta Pro supports up to 1600W of solar input from a variety of panel makers due to the wide voltage range (11-150V) it supports. Having to deal with a single 35.3-pound (16kg) panel is unwieldy enough at 94.1 inches / 239cm unfolded. It does fold down flat, though, which allowed it to be easily packed into the rear storage area of the camper (aka, the garage) I had rented.

I had previously tested the 400W EcoFlow panel and Delta Pro with EcoFlow’s oddball solar tracking robot. The panel produces a maximum of 310 to 330 watts of continuous power, which is enough to charge the Delta Pro’s 3.6kWh capacity battery at a rate of about 10 percent per hour. I was lucky with the weather, enjoying mostly sunny days on all but a handful of the 21 days we were away. 330W was only possible in full sun and with the panels positioned at 90 degrees to it. But without the help of the solar tracking robot, my charging rate would hover closer to 100W because I was too lazy to move the panels more than three or four times each day.

Charging anxiety for van lifers is akin to the range anxiety felt by EV owners. Fortunately, EcoFlow gives you multiple ways to keep on top of your inputs and outputs in real time. The Delta Pro itself is fitted with a large LCD that tells you which ports are active and how many watts they’re using. Otherwise, EcoFlow will sell you a dedicated display panel you can mount on a wall or just use the iOS and Android apps which is what I did. The apps connect over Bluetooth or Wi-Fi; the former is great from inside the van, while the latter (when connected to my mobile hotspot or Starlink RV) let me monitor my power situation from more than 100 feet away.

I don’t know if access to this data reduced or increased my anxiety, but I found it to be compelling and addictive. Seeing the solar input drop off was also a good reminder to realign the panels to the sun. The app maintains a historical graph of inputs and outputs but only for as long as the app is open. That’s a shame because I’d love to see a daily archive of that data to better understand my consumption needs.

During my three weeks away, I was able to rely almost exclusively on that 400W panel to keep the Delta Pro charged, usually finishing the day with the battery at close to 100 percent. I plugged into shore power just once to test it and marveled at how quickly the battery filled by drawing just over 2600W. The heavy-duty three-pronged jack used by my RV is the one input the Delta Pro doesn’t have, but my shore power cable came with a two-prong European plug adapter. I also plugged the Delta Pro into the van’s 12v car socket while driving in my quest to always be charging — it very slowly moved the needle, but I was happy to have it.

Despite using a wide variety of devices that needed regular charging, including a GoPro, two MacBooks, a handful of phones, a projector, a portable Nespresso coffee maker, Starlink RV internet, and an e-bike, my battery never dropped below 55 percent with diligent charging despite having to plug the e-bike’s depleted 615Wh battery into the Delta Pro every few days.

The Delta Pro could also power much larger devices. For example, on one occasion, I had to plug the Fiat Ducato directly into the EcoFlow battery after the van’s recreational battery died while parked in the same spot for a few days (it only charges off the van’s alternator when driving). The Delta Pro allowed me to keep the van’s water pump, lights, and two fridges operating off-grid for days longer as a result.

For kicks, I even plugged a house into the Delta Pro. Not just any house, mind you, but a tiny house that’s built to exist on its own in the Swedish forest, far away from the public grid. It worked as expected, feeding electrons into the home’s even larger battery over the van’s shore-power cable and adapter. The forest house typically receives power from the six 320W solar panels mounted on the roof to charge its 4800Wh battery during the long Nordic days of summers, making the 400W / 3200Wh Delta Pro kit I was traveling with a capable backup solution.

Solar generators like the Delta Pro certainly have their benefits (can be used indoors, run quiet and green), but similarly specced diesel generators are usually cheaper and can run for as long as you have fuel, making them a more practical backup for such a home in the dark Swedish winters. But if cost is no option, EcoFlow does sell that dual-fuel generator mentioned earlier that automatically kicks into action if the Delta Pro’s battery drops below a user-defined threshold. Like I said: ecosystem.

Other observations:

The battery itself isn’t waterproof (you can buy a waterproof cover), but it’s still very durable. We had it parked in between the captain seats where my dog would claw at it and use it for his travel perch. And the wheels stood up to gravel, dirt, and sand while being dragged around by the telescoping handle that never buckled under the stress. The Delta Pro’s fast charging inputs create a lot of heat which means its fans can get quite loud. That can be annoying in the confines of an RV or tiny home. It’s much louder than the smaller, slower charging, and less capable Jackery solar generator I reviewed in July. Fortunately, there’s a button on the back of the Delta Pro that can reduce the fan noise, but this also slows down the charging speed. You can also reduce the charging rate in the app by setting it to whatever wattage you prefer. As if six charging methods wasn’t enough, EcoFlow has a wind solution “coming soon” for the Delta Pro. That could be a lifesaver in a storm when the sun is blocked out and the power grid is down. The app can be buggy at times. For example, setting the max AC input charging rate won’t commit until you kill and reopen the app. But overall, the app is very good, giving you nearly full control over the Delta Pro battery and its ports.

I just returned from a day at the largest RV show in Europe and overheard three random conversations by attendees who were raving about their EcoFlow setups. One or two would be a coincidence, but three is remarkable. I can understand why.

EcoFlow is an interesting company that makes a compelling ecosystem of portable power solutions suitable for job sites or people who enjoy going off-grid for just a weekend or as a way of life. Its easy-to-use products can also be your insurance policy against blackouts if that’s a concern where you live.

Products like the $3,699 Delta Pro (which is often on sale for less) and its huge storage capacity, high AC output, portability, insightful app, and wide range of ports and charging options let people go further off the beaten path for longer periods of time. Return home, and it can then be used as emergency backup power for everything in your house. That type of freedom, unencumbered by worries about how you’ll keep all your devices for work and play powered up, can be truly liberating.

Photography by Thomas Ricker / The Verge