A number of firms offer a replacement battery for the Sony NP-BX1 battery which is used in the Sony RX100 series cameras. I have the Sony RX100 VII and am very happy with it. Owners of this camera know that the camera “drains” the battery rather quickly. The capacity of the Sony brand battery is 1240 mAh. The capacity of replacement batteries varies from 1100 mAh to 1800 mAh. To the first order, one might expect 1800 mAh batteries to operate almost 50% longer than the Sony battery. In casual operations, this didn’t seem to be the case, i.e., they all seem to give me about the same run time.

So I decided to perform a test of the various batteries I have to learn the “truth”. The test process was to set the RX100 VII to have its display ON for 30-minute intervals and count the number of intervals required to discharge each battery. I note that each tested battery was first discharged in the camera and then fully charged using the same charger for all the batteries. The time between intervals was no more than 10 seconds. A photograph of the batteries tested is shown below.

Battery Capacity Time to discharge
1100 mAh 194 minutes
1240 mAh 216 minutes
1600 mAh 210 minutes
1700 mAh 215 minutes

The test results tend to confirm my earlier observation, but this test was at a modestly low current draw. When shooting, running the EVF, and operating the zoom lens, much more current is drawn albeit for short times. A further observation I made when performing the tests was that the battery capacity indicator on the camera (4 bars) behaved differently. For example, the Sony battery held four bars the longest, then three bars, and rapidly went through two and one bars before exhaustion was indicated. I suggest that this indicates the internal resistance of the Sony battery is the lesser of the batteries tested.

The Sony battery is about $35 or so and some replacement batteries are much less expensive. For example, the Green Extreme is about $15. Although not tested, a pack of three DOT-01 Brand 1800 mAh is only $15 ($5 each). The 1600 mAh battery tested was the FirstPower and a pack of 3 batteries and a triple cell charger was a total of $20 on Amazon.

Bottom Line: Don’t waste your money buying the Sony or other expensive replacements. The much less expensive batteries appear to work adequately. For the price of a pair of Sony batteries, you can have a pocket full of low-cost replacement batteries that will let you operate for a long time!

As I mentioned, there appears to be a difference in the internal resistance of the various brands of the NP-BX1 type batteries I evaluated. The Sony seems to be the better although all of the other three provide "good enough" performance. You might be amused that the Lithium based battery was patented in Britain in 1976 by Whittingham. However, the first viable Li-ion was developed by Dr. Goodenough while the Chemistry Chair at Oxford during the late 1970s and early 1980s. He solved the issues with Whittingham's approach. And yes, his name was really Goodenough!

As I mentioned, there appears to be a difference in the internal resistance of the various brands of the NP-BX1 type batteries I evaluated. The Sony seems to be the better although all of the other three provide "good enough" performance. You might be amused that the Lithium based battery was patented in Britain in 1976 by Whittingham. However, the first viable Li-ion was developed by Dr. Goodenough while the Chemistry Chair at Oxford during the late 1970s and early 1980s. He solved the issues with Whittingham's approach. And yes, his name was really Goodenough!

I used to have a little wall sign in my class room.
"The enemy of good is not bad. It is perfect."
Good enough is well, good enough!
After decades I still have a problem getting my wife to understand that. Her family associated quality with price and believed that if you could afford it you only got the absolute best. Even something you were buying for a one off project.
Over the years I have bought a lot of "good enough" tools for projects because it was a one time thing with me and I didn't need a tool that would last decades of regular use. And a lot of those supposedly "cheap" tools are in my garage after decades and still perfectly good since they seldom get used and I am careful (read as cheap skate) when I use them.

A few years back one of the tech magazines did an article on batteries, esp those for advanced electronics like cameras.
At the time there were only about 6 companies/factories that produced over 90% of the battery cores on the world market and all those other brands bought cores from them and assembled batteries with various brand names. Often one factory turned out multiple brand names but had only one battery design. This was especially true for the numerous "house brands". All assembled in one factory, with cores from one company but different names on them. After reading that was when I started to use "Wasabi Power" batteries. It is a Southern California company and the batteries were totted as using "all Japanese made cores". The review stated that while their design only lasted about 3/4 as long as OEM(Canon in my case) they only cost about 1/4 to 1/3 as much depending on where you bought them. The article concluded that at that price difference a given amount of money in Wasabi batteries lasted about 50% longer than OEM batteries costing the same amount. You just changed batteries more often. They suggested battery grips on your camera. So I started getting grips that would fit all my bodies. Besides the grip vastly improves the holdability of the camera as long as you didn't mind the size and weight. Well I am now 77 and just starting to think about smaller and lighter - not because I can't carry and use them but because I can't get as much gear in the camera bag and a camera with grip swinging on a neck strap is starting to bug me.
My newest bodies; an RP full frame and R7 crop sensor don't have an available battery grip anyway.

So only buy the third party batteries that have the best customer rating and reviews. In my case that is now Wasabi and Kastar - I have cordless phones on the home line that have Kastar replacement batteries going on 10 years old in them. I bought two full sets back them and the second set is still in the drawer unused. Oh well the double set (one wired base station and 4 unwired phones on the home line) cost 1/2 the phone brand OEM battery price for 4 batteries. So even if the ones in the phones and the spare set die of old age I still saved money.