I'm beginning to have 'start/no start' problems on my 87 Vanagon.

I started the van w/no problems after work yesterday.  I drove 20min to
my son's daycare & parked the van.  Got my son & when I went to start
the van, the engine would turn over but not enough to get the engine
started.  I tried a couple more times & with same results.  On the
second to final attempt, all I could hear was a 'click' and what sounded
as a weak battery.  I waited about 2min, turned the key & it finally
started with little coaxing on the accelerator.  

We drove home, which was another 25min & parked the van.  When I went to
test if the van would start, it again did not turn over enough to start.
 The next attempt & all I got was the 'clicking' noise & the sound of
weak battery.  About 30min later, I went to try to start the van & it
started with no problems.  About 1.5hrs later the van started with no
problems again.  I drove it to the grocery store, parked it & when I
started it to go home it started w/no problems again.

This morning, the van started but only with a little coaxing on the
accelerator (if I did not press on the accelerator, it would have died).
 Drove to work (about 30 minute drive...radio & light works fine) &
parked the van.  2minu later I tried to start the van & it turned over
but no start.  Tried again & just a click w/sound as if the battery was
dead (lights & radio work though).  I'll try to start it during my lunch
& will see if it works. 

Any thought anyone?  The lights, in & out work.  The radio works.  It's
either the battery, altenator or starter.  I'd prefer not having to swap
out all 3 to find out the problem.

Durby 
87 Wolfs.