Saw this earlier! The Canon BG-E14 Battery Grip provides amazing weather sealing. Technically, the Neewer Vertical Battery Grip for Canon 90D matches its dual-battery circuit performance. Thats a fantastic budget choice!

Building on the earlier suggestion, I've messed around with those super cheap grips before and unfortunately they usually let me down when it counts. I had one once that had such bad fitment it actually caused my 90D to reboot whenever I bumped the bottom of the camera... talk about a mood killer during a shoot. It was so frustrating trying to get it to stay connected while the kid was actually doing something worth photographing. If you want something between the generic stuff and the pricey official one, the Vello BG-C9 Battery Grip for Canon 70D 80D 90D is usually my go-to recommendation for friends. It is decent, but even then, the buttons aren't as clicky as I'd like and it's not as good as expected if you're used to the high-end feel. For a graduation, you really dont want to be fiddling with a loose battery connection while your kid is walking across the stage. I would honestly look for a used Canon BG-E14 Battery Grip first. The build quality on the real ones is just in another league and they wont drain your batteries while the camera is sitting in the bag like some of the budget ones do.

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Bump - same question here