I am planning to buy a few back up batteries for my a7r iii. Which brand do you recommend and which one to avoid?
For paying work I still recommend using the camera manufacturer batteries (true OEM) when possible. Today's batteries are "smart" partly because they integrate well with the camera body to show remaining power. Third party batteries don't integrate as well and there is nothing worse than running out of battery during a critical portion of a shoot.
That said, I have had very good results using the Wasabi Power brand batteries and chargers, now that I am fully retired. (I am currently using Wasabi Power battery systems with Canon dSLRs, Nikon dSLRs and Sony mirrorless systems.)
+1 for Wasabi. I use Wasabi in my pocket cameras, a Canon S100 and Olympus TG-2, and I use STK in my Nikon D90 and D7200. I don't think I get as many shots per charge with the aftermarket batteries but they cost a third or less than the camera branded batteries. After a few years I think that shots per charge has decreased more with the aftermarket batteries, but I am strictly amateur and sometimes I go for a few months without using my cameras and I don't always remove the batteries. Leaving them in circuit can be hard on the batteries. Still, for my use I am happy with both brands. I didn't hesitate to get new STK when I got my D7200 last year. If I were a pro shooting events I might go with the branded batteries to have fewer battery changes, but for my uses I am happy with these off brand batteries.
BTW I chose STK based on a few posts I saw on Dgrin many years ago. Wasabi because of a deal I saw on Amazon when looking for batteries for an Olympus E-PL1 which I have since given away. I didn't look at specs or do any studies.
Thanks so much! I may get 2 wasabi's. 2 OEM ones.