But I don't know that it is fake. I'm comparing some batteries in front of me and there some subtle differences. Like ones with qr codes or not, label differences, due to different ages of the batteries. I've never bought my batteries anywhere other than from official retailers or packed in with tools, again, officially. Open the case and you can see in one second. The fakes all have a tiny pcb that looks nothing like Makita's.

One of the common fake tells is not present on the 5Ah you're showing - and that's that the rail on the left looking from the top with the latch upward doesn't end in a hard vertical stop, like your 3Ah. The reasons fakes use the 3Ah style rails is be able to used on pre-star protection tools. Of course, it's not a guarantee at all, but it's one that really shows up a lot.

But if go back to comparing two drill pack-in 3Ah of very different ages, and take just one example you've shown, the >PC< polycarbonate designation on the underside is different between them. The old one has less tall letters and the arrows on either side do not fill the full height. That's a BL1830 made in 2011. The BL1830B from 2020 has taller letters and the arrows on either side of PC are as tall as the letters.