I have two Ozito Power XChange 3.0Ah, 18V LI-ION batteries, which I use for my lawn mower.
Since they reached their end of life after 6 years I want to replace them and I saw that Bunnings sells them as 3.0Ah and also as 4.0Ah. I wonder if they are the same size and 4.0Ah would fit into the same slot.
Welcome to the Bunnings Workshop community @gezza. It's a pleasure to have you join us, and many thanks for your question.
As long as your current batteries have Power Xchange written on the side of them, then you can replace them with the Ozito PXC 18V 4.0Ah Lithium-Ion Battery. The slightly larger 4.0AH battery will fit in the lawnmower without issue.
Please let me know if you need further assistance or have questions.