My only experience with Watson batteries was several years ago with my 1D Mark II. B&H was back ordered for the Canon battery and I bought a pair of Watson batteries from Amazon and they sort of worked. They would perform properly unless I took a sustained RAW burst (and the 1D Mark II didn't have a very deep burst in that mode); after 6 or 7 frames the camera would lock up. With a burst of less than 6 it would never lock up but you could see the battery indication for a fully charged battery jump from the "near dead" indication back to fully charged when you released the shutter button indicating that those particular batteries couldn't sustain the current needed by the 1D Mark II during a burst causing supplied voltage to drop below a critical level. I replaced them with Canon batteries.
I have a Watson charger for my XF-400 and it works beautifully so no complaints about it. And the batteries were OK in my camera in the single shot mode and I found they held a charge sitting on the shelf longer than the new Canon batteries I bought to replace them but they weren't good for sourcing a sustained higher current draw and definitley weren't good for shooting sports. I never turned on IS when I was using them which would have probably created an immediate fault between IS and servo AF. But it is likely the Watson batteries are fine for other applications and as I recall the cases and locking mechanism were well made so they weren't just a poorly thrown together knock off.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
