The battery problem and how to solve it

 A big plus of the OM1 is that you can take photos even without a battery. But if you want to flick the On/Off switch and use the exposure meter, you will need one. And therein lies a bit of an issue.

When the OM1 was made, it took a mercury PX625 battery, giving 1.35v of power. But mercury batteries are no longer available, and that fact alone might put some people off using an OM1. However, various solutions are on hand.

First of all, a WeinCell MRB625 is the same size & voltage. I have not tried one of these, but I have read that they only last a few months.

Second option - modern batteries, the same size as the PX625, are available, but at a higher voltage of 1.5v. An example is the LR9 EPX625G. The higher voltage will cause the meter to read incorrectly (opinions vary on how much it will be out by), but by adjusting the film speed setting you can get it back in line again - a bit of testing on a sunny day should give you an idea of the change required. However...while alkaline batteries do tend to have a long life, their voltage reduces over time, so that will cause readings to be out again. Better are Silver Oxide batteries, which stay at the right voltage for longer, and then drop off fairly quickly. The S625PX or SR09 is once again the same size as the old mercury battery, but 1.55v, so the ASA setting trick comes into play again.

Third option - an MR9 voltage-reducing adapter, which is a battery holder, the same size as the mercury battery, and takes a modern 386 1.55v silver oxide battery. The adapter contains a tiny circuit which reduces the voltage down to the 1.35v that the OM1 expects. The adapter is relatively expensive (about £29 at the time of writing), but should last forever, and the 386 batteries are cheap. I bought one of these a few years ago for another camera which had originally taken the 1.35v batteries, and it is now in use in an OM1, with no problems.

Fourth option - a diode can be added to the battery wiring underneath the bottom plate of the camera, to reduce the voltage in the same way as the MR9 adapter. My other OM1 had this job carried out before I bought it, with a small spacer added to the battery compartment so that it takes SR44 silver oxide batteries (1.5v), quite a bit cheaper than the SR09 mentioned above. 

So the lack of the original battery is not the end of the world. Which option you go for might depend on how much you are willing to spend, and how often.

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