Sudden dead battery - Is this common?

Everything was going along fine; I parked my car for a few hours.
Never left anything electrical on, and when I got back and tried to start the car the battery was completely (And I mean completely - no dome lights, dashboard lights, etc.) dead [The battery is 7 years old]. I got a jump and with the alternator supplying electricity everything was fine. After driving for an hour when I got home the battery was just as dead. I put a voltmeter across the terminals and it only registered 7.5 volts (I would have tested it with a hydrometer, but the battery is completely sealed). I have since put in a new battery and everything works fine.

I thought batteries died gradually. How does a battery die suddenly, and does this happen often? With any other battery I owned it gradually deteriorated.

Yep. They die quick and right now with cars running scads of electrical items: computers, electric pumps, injectors, always-on driving lamps, etc.
Mine, in sunny (read hot!) CA, only lasts about 2-3 years and it doesn't matter how many months they guarantee it for, they just the pro-rate warranty exchanges for another. Last one died between first and second gear crossing an intersection. Just shut down completely and had to push car out of intersection. There is little, or no warning now when they go.

Oh yes, always charge up a new one too, else you will never achieve full charge. Supposedly the Hawker Odyssey batteries are the best going now for high heat environments - but very pricey.

Yes. Since it happened to me a couple times 20 years ago, I just replace the battery on a schedule every 4-5 years as a maintenance item. Best to replace it on my terms than on it's term. Since I started doing that, it was the last time I was ever srtanded by a dead battery.

It WAS deteriorating; you just didn't notice it. You lost a couple of cells.

Actually, you got about 2 more years than I ever get with a battery. Keep the terminals clean, and don't sweat it for another 4 years or so. <g>

I have had two die on me in the summer. Car running fine, then go back to start it and either nothing, or a small click. I think what happens is a internal lead bridge between the cells opens up or gets a high resistance contact. They don't make them like they used to.

Seven years is about all the warning a guy can expect. What makes a person that owns a volt meter and a hydrometer go seven years on a battery? I would bet that a check of that battery a month ago or a year ago would have shown low voltage and low capacity. We'll never know.

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They can go suddenly. It can gather enough sediments and develop a shorted cell(s). I'm surprised you have a _completely_ sealed battery from seven years ago. Most maintenance free battery have a pair of lids on top that can be pried off from top w/o a damage and you can use a hydrometer.

When you install a new battery, check that there's 13.8V or - 0.2V at idle. If it's running lower than this, your battery will be chronically undercharged and will die prematurely.