Thanks for pointing out what I should have spelled out.
Not anymore. They are, or already have been in most places, replaced by either depleted electrolytic cells or the newer recombinant low maintenance cells. This is due to federal laws regarding hazardous chemicals and annual permits required for flooded cell plants (big plastic jars full of sulfuric acid) and precautions mandated by the Feds regarding dams around the plant and drains into underground holding tanks to keep the acid out of the environment if it leaks out.
Now who is comparing apples to oranges. I never said lead-acid cells loose 20% annually. Go back and read what I typed. In fact, I never mentioned lead-acid battery plants.
Again, you honestly and truly don't know what you're talking about. I could name 4 or 5 scenario that would cause such a failure at what you would call a "manned site". In fact I was instrumental in restoring a junction site that lost AC power, Control center didn't notice, Gen set was overloaded and wouldn't take load. They dispatched me 5 hours after the AC failure and I was 3 hours away. I got there 10 minutes after the site went down. It took me about 1 minute to reduce the load, reset the Gen set and get the site back up.
Weather conditions, even here in Ohio, can make it impossible to get to a site or for the utility to restore power for days on end.
Interesting! Who mentioned deep discharge of the Prius battery pack?
Bruce, get your act together and don't jump down someone's throat until you have read and UNDERSTAND everything he said.
A reduction of 50% capacity is a reduction of 50% capacity regardless of the cell's chemical composition. Once the plant has lost about 50% of it's initial capacity, it will have to be replaced because it can no longer supply the needed power. The only question is how long it will take the plant to reach that point.
Jack