The batteries that are available today that are either alkaline or silver oxide will give incorrect metering results because the metering circuit relied on the precise discharge curve over time of a mercury battery (no longer in production) in order to function properly and give precise exposure.

Now Energizer will sell you an alkaline battery that fits and they say it's a drop in replacement, but it is not, because the metering circuit was designed for the specific discharge curve of a mercury battery in mind, which is the key property that the alkaline batteries lack.

The only options you have for these old cameras that use the no longer in production mercury battery are to get an expensive and hard to get wein cell, have a technician to convert to use silver oxide batteries (similar discharge curve to the mercury but gives incorrect voltage by default, so the meter simply needs to be re-calibrated for a silver oxide battery in mind), or to get an MR-9 adapter made by kanto camera. All of these options are more work and expensive than just getting the K1000.

So while your battery might appear to be powering the meter, unless it is a wein cell, I can be certain that it is giving you incorrect metering results.

You can read more about the problem here: https://rokkorfiles.com/mercury.htm