There is nothing wrong in connecting batteries in series to increase the
overall voltage for the application. There is no safety issue with
series connection as the batteries has no chance of fighting one
another. If a cell in one shorted, the result is a lower overall
voltage.

The problem with connecting them in parallel is if one cell in one
shorts. The other battries will try to balance the voltage and dumping a
lot of current into the bad battery cause it to produce significant
heat. Hence a series safety problem.

There may be folks claim they have don't this for years and never have a
problem. This is like saying I have been overloading my wiring at home
for years and my house haven't burn down - so is the proof it must be
OK.

- Vince

http://gipsyflies.home.comcast.net
1989 Vanagon GL Camper
1993 Mazda Miata (for sale)
1996 Land Rover Discovery
2005 Mini Cooper S

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Fin Beven
Sent: Tuesday, September 21, 2004 2:01 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Combined Optima Batteries

http://www.optimabatteries.com/publish/optima/americas0/en/config/produc
t_info/automotive.html<http://www.optimabatteries.com/publish/optima/ame
ricas0/en/config/product_info/automotive.html>

Combined Optima Batteries...

Vince....

Thanks for the response.  The little S/S screws actually don't so much
act as the contact as they do a wedge, forcing a fine contact around
most of the ring between the core and the outer ring.  Your solder
suggestion is great.  If I had any welding talent, I might be able to
fill what small gap remains, then remove the screws, and then fill that
small hole as well.

Like you, I wouldn't "preach" the combining of batteries.  I have used
the same process on sailboats that race offshore (races from SoCal to
Hawaii and Mexico) for years.  We are typically away from outside help
for 6 - 12 days at a time.  Extra weight is a BIG thing on these boats
(lighter is faster), and a dedicated starting battery that does nothing
the other 23:59:55 of the day would be avoided.

Since I never "isolate" my other battery, I could not see the purpose of
a relay or other device.  In the attached photo from the Optima
web-site, it looks like they are doing essentially what I have done.
Although, curiously, they appear to have joined their batteries in
series, producing 32 volts if we are seeing all of the batteries
involved.  What, do you suppose, runs better on 32 volts ????

I guess I'd take this as an Optima recommendation ??? for joining
batteries.

Fin.