Technical Information About 357 Batteries

• The silver oxide batteries from all manufacturers contain something like 0.3 to 1% mercury! This helps preserve the anode. Internationally up to 25mg of mercury per cell is considered acceptable.
• Although various battery books list that AgO cells lose capacity at up to 5% per annum, Energizer claims their cells lose capacity at 2% pa or less at room temperature. Sealing is now so good that tested shelf life exceeds 10years. In accelerated (high temp aging tests) the cells have even longer projected shelf life. This would means it is hardly worth refrigerating cells. (Normally ~doubles shelf life for every 10C reduction).
• High current pulse rated cells like the 357 all use KOH electrolyte. Low current rated cells like the 303 use NaOH electrolyte. Vendors like Duracell (who don't actually make their AgO cells themselves) mark their cells 357/303 and ship only the high current version. It used to be that the KOH cells were much harder to seal as the electrolyte is more active and attacks the seals and cell separators. The capacity was also a little lower as the separator needed to be thicker. This is no longer true. Why then, does anyone make NaOH cells anymore? The answer is watch vendors often demand a NaOH cell as they still believe the sealing is a problem and are worried that the KOH cells are more likely to leak and cause damage. The sealing on some vendors cells may still be problematic, so avoid generic brand cells.
• The 357 cell is capable of short circuit currents up to a couple of hundred mA when new and for short durations (<100mS).
• The Energizer 357 cell capacity under low rate conditions is higher than the nominal 175mAh rated , approaching 200mAh. (The very old data book values used to be 200mAh but this was at 35C (wrist temperature, which helps a little.) not 21C. This helps with OM4's and 2'S's which have higher "off" standby current. The 357 cell has been significantly reformulated over the years since first introduced for use on LED display watches.
• It would be interesting to compare Energizer's cells to those from other vendors. In particular an accelerated life test would be interesting and a high rate capacity test to see if there really are differences.

A very significant issue for OM use, is the change of battery internal resistance as the cell ages, and of course near the end of discharge life. This causes increased battery voltage drop at peak camera operating currents at shutter opening.

One vendor's batteries show an almost doubling of resistance after one to two years of storage. In general the resistance increases sharply in the last 20% of discharge life and is what ultimately causes sudden camera lockup in OM's. The resistance change in storage appears to depend on the vendor's process and may be the reason why certain "new unused cells" cause lockup in the OM occasionally. The resistance in the case of the watch vendor's cells, increases after a year or two, and then drops off again to closer to new values after about 2 years.

Based on Everready's longevity claims (not tested myself) their 357's do not suffer from the large increase in resistance or fail after a some years of storage. Hence my recommendation: stick to Everready.

The battery life in OM use, is probably as much related to battery resistance near end of discharge life, as it is to rated capacity in mAh. It would be interesting to run some discharge-resistance curves to compare different vendors cells.

When I asked Everready about the '76 type (SR44 size), which are shown as having a sloping discharge voltage near end of discharge, the tech support person said he thought they no longer had that characteristic, although he was not completely sure! Cells with a shelf like end of discharge curve, were engineered at one time to allow easy end of battery life detection.

contributed by Tim Hughes