I use a lot of the BLC12 Batteries. I buy the Panasonic ones; they aren't cheap but they last the longest and don't turn the camera off with no warning.
However, I do buy aftermarket batteries for testing from time to time. They often have very high ratings, and they never work very well.
A few years ago, I bought the DSTE "1600mah" battery. It had about 70 percent of the stock battery's power, and the stock battery is 1200 mah. So that's 840mah, or about half the advertised capacity.
A few weeks ago, I purchased the 1700 mah version at this link:
https://www.amazon.com/dp/B00MEAMBQU
It weighs 55 gm as opposed to the stock 50gm. Previous clones weighed 46 and 48 gm.
Now before you get excited, the extra weight is probably ballast, since you can't squeeze more cells into a battery, as a general rule.
However, after extensive testing, this battery is equal to--not better--but equal to stock. The only difference is that the shutdown curve is a bit steeper.
So it isn't "1700" mah, but it is basically a stock battery.
This was quite a shock, but I repeated the tests several times. In one test, I simply turn on the camera and record video until the battery croaks, and measure the time. Both the stock battery and the DSTE run the G7 for two hours of video, sometimes a few minutes more, sometimes a few minutes less. So, finally, an inexpensive option. At least for this batch. Also, see my post on the cheap external battery that will run your camera all day.

I purchased this one.

https://www.amazon.com/gp/product/B073XYYYWR

There's another model that has two USB inputs, so you could use two power banks or use one and draw more amps.

I was skeptical, and the packaging made me even more so, cardboard & crinkly shrinkly, but I plugged it into my cheapest 5200mah power bank and measured the voltage. 8.8 volts, which is just about right (I've gone as high as 9.2, but prefer not to). Notably, the needle on my trusty voltmeter did not wiggle. Also noteworthy, it didn't seem to need the recommended 3 amp draw. It comes with a 3 amp wall wart if you just want to plug the camera into the mains for power.

It comes with a bog standard dummy battery. The step up converter is tiny, not much thicker than the cable. Plugged in the camera (Panasonic G7) and waited. The 5200mah power bank ran the camera for 156 minutes, or two and one half hours. Not bad--you are going to lose some power in the conversion so don't skimp on the power bank. I'll do some tests later with my RAV 20,000mah bank.

Camera ran cooler than expected.

So there you have it, easy, lightweight power from USB. I had been using 9 volt packs with stacks of Panasonic 18650 cells (runs forever....). But this is really easy.

You can buy adapters for most cameras, and considering the fact that it comes with a dummy battery, the price is cheap. Will it burn out? Interesting question.

[Added formatting and photo, VK]

Just wondering whether anyone has had any experience with using official GH2 batteries from different regions from where they bought their GH2 from.

I.e. Using a Japanese GH2 battery in an Australian GH2.

I only ask as there's two different GH2 battery models: DMW-BLC12 (America / Japan) DMW-BLC12E (European / Australian)

The power output is the same on both models. (7.2V 1200mAh 8.7Wh)

Thanks.