Back when the Makita 18v LXT stuff first hit the market, they had far fewer tools. The first ones were all 3ah battery. After a few months, they released a more "home owner" oriented drill and driver with 1.5ah batteries, at a reduced price. They were white/black instead of the usual Makita blue, but otherwise very similar. I decided that I liked the smaller/lighter batteries better, so I used them with the blue impact too.
What I found out over time was that there was a difference in the batteries themselves. There was a little tab inside the sliding grooves of the tools that was different on the tools that needed the higher amperage. The smaller batteries would not fit in them. The big 1/2" hammer drill, 6 1/2" circular saw, and a few years later the jigsaw would not take them, yet because of the way this groove works, the bigger batteries would fit anything.
This was all more than 15 years ago, now battery amperage has gone crazy and they are stacking batteries to get 36v too.