There’s a lot of online debate about third-party batteries. Should you buy them? Well, as with most things, it depends… Here’s a video that was just posted by FStoppers about GH5 batteries.
There are different qualities of third-party batteries and I definitely don’t recommend you buy the cheapest ones. Those really cheap batteries often have reduced capacity, greatly reduced life-span and can sometimes damage your camera: they can leak, explode or simply expand and damage the battery compartment or get stuck.
Some of the better batteries (I use a couple of Wasabi batteries in my E-M1) seem to be safe and work reasonably well. However, I find that my Wasabi batteries do not hold their charge as long as the Olympus batteries. In other words, if I leave a fully charged Wasabi in my bag for a few weeks, more often than not when I try to use it I find it dead. This has never happened to me with Olympus batteries.
With my Nikon D700 I also used some third party batteries but they stopped functioning all-together after a few months whereas the Nikon batteries easily last 3 years. So the savings from third-party batteries is not what it appears to be at first glance.
Another potential issue is that some third party batteries do not communicate correctly (or at all) with the camera, so they may show full charge when in fact they are about to die. Worst is that as in the video, the camera may never get a warning so it cannot safely shut down and save your files, causing serious data loss.
Also many of these batteries advertise higher capacity, but in every case I’ve looked at so far, that claim is not accurate. They are always equal or lesser in capacity to the genuine batteries.
So if you’re going to buy third party batteries I recommend you stick to the better ones. I have good luck with these Wasabi batteries for my Olympus E-M1.