Ego string trimmers
The amount you need to mow can determine the battery you might use. There is no minimum. 2.5 works well for 20 minutes. 5 obviously longer. I use a 5 for my front and back yards and it is generally enough to get both done on one charge. And as Ken said, any EGO battery will work in any EGO tool.
Using the provided 5Ahr battery in my LB5800 blower, it performs excellently. I put a 7.5Ahr battery in it and it gets turbo charged. Big kick back, louder (faster fan speed), blows them twigs right outta the grass. So if a larger amp/hour battery of the same voltage makes the motor speed on a blower increase markedly wouldn't ya think that a smaller than prescribed 5Ahr battery in a mower would spin the blade at reduced RPMs? And, perhaps, the likelihood that any challenge such as a taller patch of grass would bog it down faster. Any EE thoughts from EGO or the Expert Peanut Gallery?