I learned something this morning, after not learning it for some time now. My large capacity (6.0 AH) Makita batteries don’t fit on my portable Makita angle grinder. At first, I thought it was some minor thing like when I’d bought some off-brand batteries and they just didn’t fit the slide very well. But NO!

One of the things I’ve consistently noted about the angle grinder is that it appears to have a thermal cutoff circuit in the tool, and will shut down the tool after heavy (or sometimes, not so heavy) usage. Working outside in the desert in summer causes it to trigger regularly, which is annoying to the point of unusable sometimes. I also note that it only seems to happen on old batteries or batteries that don’t have much charge left.

I bought a few months back some Makita 6.0 AH batteries. Brand new. Came fully charged as well in original Makita packaging. Cost plenty. Interestingly, they fit on all my tools but the angle grinder. And just now, I learned why: on the angle grinder, there’s a plastic nub protruding on the battery slide that prevents the battery from engaging. See Figure 1.

On-line, people talk about filing/cutting the nub off, and that obviously solves the issue of the battery mate. Bu others pointed out there’s circuitry missing in the older tools that is important to managing the battery capacity and preventing over-depletion. Ok, I’ll buy that, except:

I bought most of my Makita tools as a kit, back in 2006 or so. Angle grinder, circular saw, drill, impact driver, flashlight, charger, two 3.0 AH batteries, and the all-important “sawzall” tool. And none of them, except the grinder, have that nub! Just last month, I bought an orbital sander and a mini-shop vac. Interestingly, the orbital sander has a microswitch where the nub would be, and a third contact (Figure 2). So, that appears to allow the sander to detect the difference between batteries, and apparently do something about it.

I am convinced that there’s a good technical reason for the nub, but since it’s only on the grinder, and the grinder’s more than 10 years old, that I just might consider removing that nub and taking the risk that the tool goes up in flames.

UPDATE: I actually found and read the manual. Figure 3 shows the important bits about overload and battery indicators.

That certainly makes sense based upon my observations. And here’s a bit of unintended irony:

It got to 117 deg F yesterday at the site. Not sure how to manage this item. Wear gloves and eye protection, to be sure!