'01 Blazer: Intermittent starting problems

Me again... I'm continuing to have a problem with my '01 Blazer (4.3L) that I thought I had cleared up last week. Here's the story: The wife takes it to work one day last week when we had some bad
weather. She said it turned over slowly when she went to work, and at the end of the day, it just went "click, click, click" when she tried to start it to come home. We went out and jump started it without any problems. Got it home, pulled the battery and took it to a local shop. The guy there said that it was taking a charge, but to put it on a charger overnight... which I did. The next day, the vehicle popped right off perfectly. I drove the vehicle into town and had the guy at the battery shop test the battery again, test the charging system and check to see if there was any unusual draw on the battery when the vehicle was shut off. Everything checked out ok. So... I've driven the vehicle for a week now without any problems.
Today, we took a little 60 mile (round trip) jaunt to do some major grocery shopping, etc. We made several stops. When we returned home, I parked the vehicle closer to the front door to make the unloading of our bounty a little easier. I shut the vehicle off and unloded our goods. About a half hour later, I attempted to start it so that I could move it to its rightful place in the driveway. I got the "errr... err... err... click... click... click..." of an engine trying unsuccessfully to fire.
Anyone hazard a guess as to what's going on here?
Thanks!
P.S. Thanks to all who gave input about my $12 spark plug question!
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Could be one or more things:
How old is the Battery? Was it load tested when it was Hot. If its past its warrenty and not a $80-$100 battery then its most likely beyond its service life. It should measure 12.65V at rest, no load , fully charged. ( standard battery voltage) If it measures less then it may be sulfated. I'd say 12.45 volts at rest will cause problems when its fully charged as measured with a hydrometer. See http://www.batteryfaq.org/ to brush up on battery health.
It seems like the battery cables are good, since once the battery is charged it starts.
Alternator is not working all of the time. Is it still the original one? Did you replace it with a rebuilt? Always get a dealer part, they have the latest upgrades, where re-built's do not. At idle the voltage should be 14V . GM's idle voltage spec is all over the place, thats another story.
Cheers
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On Sat, 2 May 2009 22:48:38 -0400, "Martin Riddle"

years now (it had 126K on the clock when I bought it, it now has 138K) and have not replaced the battery myself. It is an AC-Delco, and when I pulled it last week, I noticed that it didn't have one of those month/year things that indicate purchase/in service date for warrantee purposed. As such I assumed it might even be the OEM battery, but I could be wrong.
Again, my history with the vehicle has not afforded me the opportunity to replace an alternator on it, either.
If I get it running again, i will have my mechanic check these issues out next week when I'm having him put those $12 spark plugs in the thing! HAHAHA!!
Thanks for the tips!
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On Sat, 02 May 2009 21:00:36 -0500, Phil McCracken

Just a follow up...
Went to get all that work done on my Blazer this morning. My mechanic diagnosed the starting problem as a bad starter which was, for whatever reason, drawing current from the battery. So, a remanufactured starter is going on Thursday morning.
A P.S. regarding the $12 plugs... He pulled a couple plugs and determined that I did not need them replaced at this time.
Thanks to all for your time and input!
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