Dennis,
I wonder the same thing when the issue came up in my westy conversion, if to do the venting or not.
I had thought the batt vented during discharge as well? and thought while sleeping / living in the van
one may be exposed more so?  

I cooked a battery with my 15 amp charger in one of my vans during a hot summer week. 
I had let the self adjusting charger stay connected with the cord going through the sliding window. 
I forgot about it and left it charge for days and days. Till one day I could actually "smell" the fumes 
from the battery outside the van. I rolled the slider open to see the charger pegged at 15 amps and
the fan fully engulfed in battery fumes. Took the battery out it, and it was so hot I could not even touch the 
outside of the plastic case. 

How close to creating a "vanagon explosion" did I come?

Doug

  ----- Original Message ----- 
  From: Dennis Haynes 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Friday, March 10, 2006 10:11 AM
  Subject: Re: 2nd battery; two questions

  Only the campers had the sealed and vented battery boxes. Why? I don't know. Beetles for years had the batteries under the back seat without venting. Later Audis used a battery with a small vent tube. Many group 41 (Vanagon) and group 42 (Beetle, Gas Rabbit, etc) are available with this feature.

  Normally, the venting is not a problem and a battery will only off-gas while charging. The normal 13.8 charging voltage does not create much gas. In crease the voltage to 14.5 and gassing will occur. If a battery has a cell sort out, the remaining cells will gas vilently and electrlyte can spill over. This can make a real mess.

  A typical group 41 battery is good for ~ 65 amp/hours.

  Dennis

  ----- Original Message -----
  From: Mike Collum <collum@VERIZON.NET>
  Date: Friday, March 10, 2006 12:55 pm
  Subject: Re: 2nd battery; two questions

  > First, let me point out that my '84 7 passenger came from the factory
  > without a sealed or vented battery box for the MAIN battery.
  >
  > My '85 Westy has the vented box for the main battery only.
  >
  > I installed an ordinary group 41 battery as my aux battery under the
  > driver's seat in the Westy (box not sealed or vented) and I've had no
  > problems with fumes.  I have my aux battery feeding the interior
  > lights,the sound equipment, the cigar lighter, etc.
  >
  > Mike
  >
  >
  > Gerald Masar wrote:
  > > For those who have installed a regular group 41 (or other size,
  > same type) battery, do
  > > you have any problems or concerns with fumes, given that the
  > compartment under the
  > > driver's seat is neither sealed nor vented.
  > >
  > > How does one figure out the amp/hour rating of a battery if it
  > is not listed and the
  > > sales person hasn't the foggiest idea what you are talking about?
  > > Or, what are the approximate amp/hr ratings for run-of-the-mill
  > group 41's and
  > > Optimas?
  > >
  > > Thanks,
  > > Jerry
  > >
  >