Try your brains and knowledge on this one!

'83 Vanagon, water cooled.  Have 2 batteries with selector switch. When
cold, starts normally on battery #1.  When hot it will crank, but not
start.  After a number of tries, the battery runs down and can't get
passed TDC.  At this point, switch to #2 and engine starts.  Battery
checking machine: reads 12.5 v, under lst start test, voltage stayed
above 9.  On second test, dropped below 9.  

Now that you are thinking battery, let's throw this curve:  When hot, if
I first open throttle all the way, then crank, it almost always starts. 
Ha!  Figure that out!

TBill

****We have enough youth.  How about a fountain of smart?****