Expandable power stations: adding an extra battery to a 1kWh station

An extra battery is worth planning for if a day of backup won't cover the outages you get. The EcoFlow DELTA 3 Plus and the Anker SOLIX C1000 each take a matching add-on that roughly doubles them to 2kWh, so you can buy the station now and the second battery later. The Jackery Explorer 1000 v2 and the Bluetti Elite 100 V2 can't be expanded, so with those you're buying the capacity you'll live with.

We haven't used any of these ourselves. The figures come from the makers' Australian product pages and user manuals, linked at the bottom, and the runtimes are our arithmetic from them.

Which stations take an add-on

The DELTA 3 Plus has one extra battery port, and EcoFlow's manual lists four batteries that fit it: the DELTA 3, DELTA 2, DELTA 2 Max and DELTA Pro 3 Smart Extra Batteries. The 5kWh ceiling comes from the biggest of those, which EcoFlow Australia lists as an extra 4kWh. The DELTA 3 Smart Extra Battery has only the one port itself, so you can't chain a second one behind it. For most people the 1,024Wh DELTA 3 battery is the sensible match.

Anker's BP1000 only works with the C1000. Anker's US store adds that it doesn't fit the newer C1000 Gen 2, so check which model you have before you order. One small oddity: Anker's Australian C1000 page still says expansion is "coming soon", while the BP1000 is listed for sale on the same store.

Bluetti's 1kWh Elite 100 V2 page doesn't list any expansion battery. The add-on batteries in Bluetti's Australian store are for bigger stations, such as the 2,048Wh AC200L. Its Australian product page says up to two B300K batteries take it to 7,577.6Wh, but Bluetti's older AC200L page on the same site quotes 8,192Wh with two of the earlier B300 batteries, and when we checked this month the AC200L itself showed as out of stock. Check Bluetti Australia for what's current.

The blackout sums

Say your fridge averages 60W (its energy label's yearly kWh divided by 8,760 hours gives a rough figure) and the modem draws 20W. That's 80W. We allow 15% for inverter and conversion losses, so usable energy is the battery size times 0.85.

A DELTA 3 Plus on its own gives 1,024 x 0.85 = about 870Wh, and 870 / 80 = about 11 hours. Add the DELTA 3 Smart Extra Battery and you have 2,048Wh, so 2,048 x 0.85 = about 1,740Wh, and 1,740 / 80 = about 22 hours. The C1000 with a BP1000 works out much the same: 2,112 x 0.85 = about 1,795Wh, which is roughly 22 hours at 80W.

That's the difference between getting through the night and getting through a full day and night before you need sun or the grid back. For a Queensland storm outage that's usually fixed within a day, one battery is plenty. If you're on a rural feeder that's been out for three or four days after a cyclone, the second battery starts to earn its place. Our cyclone season guide goes through how to size for your street.

Two boxes or one bigger station

Splitting the capacity into two pieces makes it easier to carry. The DELTA 3 Plus weighs up to 12.5kg and its extra battery about 9.6kg according to EcoFlow's manual, so about 22kg in total, but no single lift over 12.5kg. The C1000 is 12.9kg and the BP1000 9.06kg, again about 22kg. Bluetti's AC200L, by comparison, is listed at 28.3kg in one piece before you add anything.

The other upside is that you can start small. Buy the station for this storm season, see how far it gets you, then add the battery if you find yourself short. The downside is that two boxes cost more than one, and an add-on battery doesn't add any outlets or inverter power. You still have the station's 1,800W limit and its four AC outlets, so a bigger battery doesn't mean you can run more at once. Our EcoFlow vs Bluetti vs Anker comparison covers what each station can run.

How the two batteries charge and drain

They don't behave the same. Anker's user guide says the BP1000 powers your devices first until it's empty, then the C1000 takes over, and when charging the BP1000 only starts once the C1000 is full. EcoFlow's DELTA 3 Plus manual says the station needs to be connected to a power source to charge the extra battery, and that with a compatible extra battery attached the charging speed can reach about 2,000W.

Refill time grows with capacity. The DELTA 3 Plus takes up to 1,000W of solar, so refilling 1,740Wh would need 1,740 / 1,000 = about 1.7 hours at full input. The C1000 takes up to 600W, so 1,795 / 600 = about 3 hours at full input. Real panels rarely hit their rating, and a hot Queensland roof or ute tray cuts output further, so plan on longer. The solar pairing guide explains how to match panels to each input.

Both makers want the cable handled with care. EcoFlow's extra battery manual says not to plug or unplug the cable while the station is working. Anker says to hold the BP1000's power button for two seconds before disconnecting it during use, to avoid a short circuit.

If a 5kWh setup has you thinking about hard-wired lights and fans, read our guide to changeover switches and generator inlets before you buy anything.

Storing two batteries

An extra battery needs the same care as the station. EcoFlow's extra battery manual gives an ideal storage range of 20 to 30°C, never above 45°C, and asks for a full cycle every three months that ends at 60%. It also says the battery isn't covered by warranty if it goes more than six months without charging or discharging. Anker's guide says to check the BP1000's level weekly, charge it to full if it drops below 30% and fully charge it at least every three months. The Queensland Fire Department suggests about 40% charge for long-term lithium-ion storage, so the makers and the fire service don't quite agree. Follow your manual for the warranty's sake.

Charge both on a hard, non-combustible surface in a ventilated spot while you're home, not overnight in a bedroom, and don't use either if it's hot, swollen or damaged. Never leave them in a closed car in the sun. Our storage guide has a calendar for the off season.

On cycle life, EcoFlow's own listing disagrees with itself: the Australian product page says 3,000+ cycles in one spot and 4,000+ in another, while the manual says 80% capacity after 4,000 cycles. Anker rates the BP1000 at 3,000 cycles to 80%. For a battery that mostly waits for storms, either is more than you'll use. The LiFePO4 vs NMC guide explains what those ratings mean.

Where to buy in Australia

Buying from the brand's Australian store means 230V AU outlets, the local warranty and local support. Prices move around a lot, so check on the day.

• EcoFlow DELTA 3 Smart Extra BatteryEcoFlow AustraliaSee it at EcoFlow Australia
• Anker SOLIX BP1000 Expansion BatteryAnker SOLIX AustraliaSee it at Anker SOLIX Australia