Have you bought a generic RX-100 battery and how does it compare with the genuine one?

I've read that some generic ones can actually be as good or even better than the real batteries. Of course i'm guessing most are not worth it.

Have you bought any generic ones and found they are just as good and where from?

You may want to check with Sony.

Many camera makers will void the warranty on their cameras if a generic battery is used.

There are many reasons for this, but mostly it has to do with the on-board circuitry on the Sony, Nikon, Canon, etc batteries which regulate the voltage and amperage going to the camera.

The other issue is that generic batteries can overheat, catch fire or even explode while being charged.

Think of buying a Sony battery for your RX-100 as insurance. While the Li-Ion NP-BX1 battery may cost $50, it will last decades if you do NOT let it sit fully discharged for more than 72 hours.

I have found Sony NP BX1 batteries on Amazon for less than the retail cost. I'm sure you can too.

EDIT

Since Sony RX-100 does not use an optical viewfinder, so any time you have the camera turned on, the battery is being used to power the LCD If you spend much time displaying your images or videos on the camera, this will shorten the time the battery will be able to power the camera.

Using good energy management, you should be able to shoot up to 330 photos with a fully charged battery

I guess it's not only me who feels that Sony batteries cost like a new camera.

Generic batteries are a huge gamble. There are a lot of batteries out there that don't last as long as the original (even if with higher mAh). If you really must use generic, avoid the cheapest because those are the most likely to be problematic. Avoid the most expensive too because they are the cheap ones that were packaged in grandeur for a heftier price. Then, if you buy the mid-priced one, see if you can get at least two pieces (for more shooting pleasure) without going over the price of one original.

You take a risk when buying knock-off Chinese batteries. Some cameras detect and will not work with such batteries. Others may work but not last very long. One of the biggest problems is that the batteries can expand over time and bulge out of shape so much that they will no longer fit in the camera's battery compartment. So, you pay your money and take your chances.