Technical Information About 357 Batteries

I have been looking at various batteries to power some new products I am developing at work. While I had Energizer/EverReady technical staff helping me with information, I decided to find out more about the 357 (SR44) style batteries we use in most of the OM cameras. Some new information:
A battery vendor who makes batteries aimed mostly at the watch market told me his batteries don't last more than 4 years and quoted me a loss of capacity of as much as 10%pa. It would definely pay to refrigerate these cells! (Although not in the deep freeze).

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