Seeking Information on Cache batteries lifetimes

[Cass Witkowski]

I recently had a site using HSZ40 Array controllers. The cache batteries showed good. However, during a sub-second power outage the cache was lost. It turns out that the batteries were three years old. The recommended lifetime is two years.

The problem is that the bean counters only want to replace the batteries when the show bad in the SHOW THIS command on the controllers.

Is there any Digital/Compaq documentation that talks about cache batteries in detail. Something that shows how the cache battery could pass the controller diagnostic yet still not maintain cache during an power outage? Is there any documentation that show how the capacity of a battery falls off after it's lifetime rating?

TIA

Cass Witkowski