[Vwdiesel] Alternator - Battery - jumpstart questions

[jon.sykes at ps.ge.com]

I thought I had my charging system problem licked.  My van wouldn't start
one day last week.  Turned out the alternator wasn't charging the battery so
the battery went flat.  Alternator was putting out current but it wasn't
getting to the battery.  Turns out there was a lose wire on the battery
isolater (mine's a camper) so I guess the circuit was broken.

Anyway, I ran the van over the weekend and Monday morning.  Monday lunchtime
though though the van wouldn't start again.  Turned the key and nothing
happened.  Got a jumpstart from a coworker and she started fine.

I have a couple of questions:

a. my battery is about 4 years old.  the battery was working just fine until
the lose wire - no problems starting even when the van sat, even in cold
weather.  however, now the battery has been drained so much could it have
been pretty much worn out?  can they be drained so much that the alternator
isn't enough to get them back to normal?

b. a voltage test on the battery with engine running gave approx 12.5 V.
I'm thinking it should be over 13 V.  if the battery is almost flat but
still has the alternator charging it, should I expect the voltage to be less
than normal or should the current from the alternator as recorded at the
battery be the same regardless of the battery's condition?

c. does the battery have to be removed from the van in order to charge it?
this sounds like a big no no, but reason I ask is that one of my terminals
is stuck and I can't remove it on my own.  i don't want to spend $80 or more
on a new battery until i know my battery is shot.  i'd like to recharge my
battery first and then see if it maintains a charge or not.  in order to do
this though i have to charge it in situ.  could this do some damage to the
electrical system, cause a fire, etc?

d. if all else fails, i'm out camping and the van won't start, can i jump it
from the camper battery under my seat?  hook up the jumper cables from that
battery to the engine one?  the camper battery is almost new.  again though,
could there be nasty consequences of doing this as they are both on the same
circuit?  i'm not really sure how the isolator works and whether altering
the circuit from the camper battery to the engine battery while they are on
the same circuit could damage something?

Any help much appeciated.  I know it's a 10 year old Vanagon but I'd be a
lot happier if I could be pretty certain that the van's going to start!

Thanks!

Jon