I expected the extra battery to synchronise its SOC with the main battery but it doesn't. They get out of sync very quickly. The BMS doesn't seem to be smart enough to apportion power between the main and extra battery to maintain a synchronised SOC. This is particularly problematic when you set a charge ceiling (like I do at 80%) because it will apply the limit as an average across both batteries. So one battery could charge to only 60% while the other could charge to 100% to create an average of 80% SOC. This obviously isn't great for the overcharged battery. Worst thing about all this is that I had to work it out myself since there is zero information in the instruction manual and the EcoFlow support team didn't know what was going on either.

Great buy, we run our refrigerator and microwave off the Delta Max and Delta Max Smart Battery all the time.

Refurbished battery so far functioning same as new.

Awesome, portable and easy to use. Love it, have 2

Great product - I have a small place with no fireplace so if power goes out, this can power a space heater until power comes back on