90 camry won't start...

your battery is dead a fully charged battery is apx 13v,11.7 is apx 25% charged

How long should a battery last (years) on average...

That voltage is low. Sometimes a battery will give no warning of its impending demise. If that is the original battery you are about due.

I coulda sworn "DSPL" typ'd:

Heh, heh, heh . . . no such thing as average battery life.

I have several lead-acid batteries in vehicles, some two-wheeled and some four-wheeled. I've tried to always get good batteries for reliability, but I can tell you some last a long time, some don't. There doesn't seem to be a pattern except that if you run them flat regularly they don't.

OK, I guess 4-5 years has been typical . . . .

The shortest was less than two years on a Yuasa in my '72 Honda CB500 motorcycle before it developed an internal short (it was replaced under warranty).

The longest was a Dears Sigh-hard that lasted THIRTEEN YEARS in my BMW K75 motorcycle. Unheard of.

-Don (still amazed at that one)

Ive had 2 new defective batteries last 6 months and many 3-5 years.