>>2870924I used hearing aid batteries (1,4v vs the 1,35v of the original mercury battery) and it's only one stop off, consistently, so I use the underside of the vertical stem of the black meter dial towards the + as my good exposure mark (if that's making any sense at all to you). You need to bend the contact lip inside the battery hole just a little bit upwards to make it touch the lid.
I recently found a working mercury battery in mint condition, though. A godsend and a true miracle. Swapping it with the hearing aid batter whilst keeping all other variables the same confirmed the ca. 1 stop aberration. It's slightly less, though, so you can easily get away with just treating it like it would have a 1,35v in. You should measure the hearing aid battery after pulling off the lid and waiting for ca 10-15 minutes, as it's an air cell which has to react to air before giving off power and reach its end voltage. Measuring is important, because there seems to be some difference between some of the supposedly exact same batteries from the same package. I had one that was 1,44v, so almost an entire 0,1v too high. I'm hoping there will be outliers towards the 1,35v too, but I haven't encountered them. Also, the hearing aid batteries only last 3-5 months tops after you pull off the lid, even if you don't use them. This is because of the nature of the air cell. They're dirt cheap and easily available. Be sure to get the bulkiest ones, as they have a better fit.
There are also tutorials on the internet on how to modify your OM-1x to accept regular 1,5v button cell batteries, but do be sure to throw them out just before they go empty (which should be after 6-12 months or more, just measure the voltage every now and then) because the voltage drops in the last stage of its life.
There are also adapters and replacement non-mercury batteries (wein cells).
You can also just set the iso knob one stop lower when using hearing aid batteries, as it's only used for the meter.
