FYI, I had asked about compatible batteries for the EGO SP lawnmower. I ordered the 5ah recommended for this mower. Works now. I'm confused why my 2 ah would not power the blade but the sp worked. I love my mower.
All ego tools will operate with all ego batteries. Only the snow blower comes with the recommendation to use 4.0 or higher batteries for optimal performance.
From the 21SP manual
If your mower will not operate with the 2.0 battery you have a malfunction and should contact customer service.