My only third party battery experience wasn't a Watson but it was highly rated by reviewers. I needed a battery quickly for my 1D Mark II and my regular places were out of OEM battery stock so I took a chance . It charged and seemed to work OK until I tried to shoot some rapid bursts and it would cause the camera to lock up because the battery couldn't maintain required voltage under a sustained current load. Both of the batteries charged fine, held a charge, and would work OK for non-demanding work but since I shoot a lot of sports they weren't acceptable for my use. I can't remember the brand because I gave them away years ago to a friend who wasn't as concerned about camera performance. These were older NiMH batteries instead of the Li-ion batteries used in most cameras now.
Bottom line is I only use Canon batteries in my gear. Building batteries really isn't rocket science and they don't have to cost as much as Canon pricing but Canon does provide batteries which will meet their gear needs and quality standards. Given what I have paid for Canon bodies and glass, I am not going to try to save a little on third party batteries because the potential risk return tradeoff doesn't balance for me.
Although not common, be particularly careful with cheap and potentially poorly constructed lithium ion batteries because they can source incredible amounts of current for a short time which is what happens if they short internally and that results in a battery fire. Their peak power density is pretty amazing, that is why those tiny automotive "jump starters" can claim such high output levels. Generally Li-ion battery fires occur because of charger issues but clearances are tiny in those packs so poor materials or assembly can create big problems.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
