Do I want an Optima?

[E. Roy Wendell IV]

> I was getting ready to buy an Optima Red Top for my e//S2 and was  
> told I
> might not be doing the right thing.
>
> The battery is currently in the trunk area and I will be relocating to
> under the rear seat in a stock S2 battery box.  I figured an Optima
> would be the right choice as it is a vent-free battery and the battery
> will be in the passenger compartment.
>
> I went to pick one up at Advance Auto and the store employee told me
> that I should have a vented battery.  She said that a vented battery
> would exhaust the fumes outside the car.  If I had an Optima I might
> exhaust any fumes inside the car - not good.
>
> OK, OK, I know...it was a discount auto parts joint with a likely
> less-than-pro clerk, but it did make me think.
>
> Do I need an Optima? (I guess not since the stock S2 battery was  
> vented
> - the vent hose in still in the box I bought)
>
> Do I even want an Optima?
>
> TIA,
> Dave Kase

I know I'm weighing in a little late on this one (been busy fixing  
airplanes) but because I have a lot of experience with these things I  
wanted to go on record anyway. My school has an electric powered open  
wheel race car that has 28 Optimas on board and we have multiple  
battery packs. We are constantly using, capacity testing, and  
charging these things.

What they are not is "sealed" "dry cell" or any other adjective  
Optima, their promoters, or self proclaimed experts apply to them.  
They are a lead acid battery at the core. They do have a liquid  
electrolyte of sulfuric acid. If you poke a hole in the side of the  
case acid will not gush out of the hole but if you poke your finger  
in you will get acid all over it. This is because the space between  
the plates is filled with fiberglass mat. The mat wicks up and holds  
the electrolyte but at the same time allows the various ions within  
it to transfer between the plates thus requiring less electrolyte  
than a conventional lead acid battery. This class of lead acid  
batteries is know as AGM for Absorbed Glass Mat and there are many  
others including the Concord, Hawker Genesis, Odyssey, and others.  
The unique feature is the fact that the plates for each cell are  
wound up into a cylinder rather than just left in a rectangular  
shape. AGM batteries in general have a lower internal resistance than  
a conventional flooded cell battery and therefore a higher maximum  
current. This feature is useful in really really cold climates or  
very high demand situations such as electric race cars or starting  
jet engines.

Now to the "sealed" part of the equation. They are not technically  
sealed but are instead part of another lead acid technology called  
valve regulated gas recombinate batteries. In this respect they are  
like all "maintenance free" lead acid batteries where the gasses that  
are generated during normal operation are forced to recombine into  
water by way of pressure. This means that the case is under  
considerable pressure during normal operation which for safety  
reasons means that there must be a pressure relief valve. If you look  
at the top of an Optima you will see two white discs that are in fact  
filters that sit on top of the pressure relief valves. If the  
internal case pressure gets high enough these valves will open and  
vent gasses if the batter is upright and liquid if oriented any other  
way. If there is any discoloration of the disc then the battery has  
vented at some point and due to the decreased electrolyte content  
will have a reduced capacity. Granted, during normal operation this  
won't happen. The listed exception is excessive charge current which  
produces gas at too rapid a rate and therefore the battery vents.  
This would occur is the voltage regulator failed in a short condition  
which is fairly common. I have personal experience however of an  
Optima venting under discharge and as it was installed sideways there  
was a puddle of electrolyte in the battery box. That battery went  
straight to the recycle pile. The discharge rate wasn't excessive but  
it was a sustained discharge such as would occur if the charging  
system failed.

Now as to my opinion. While interesting from a technical point of  
view, I don't see any advantage of spending the extra money on the  
Optima for your application. It's not lighter than the standard  
battery and you don't require the high current rating because your  
starting system was designed for conventional batteries. If you were  
looking to install a much smaller battery to save weight than an AGM  
battery makes sense because they have a much higher CCA rating than  
an equivalent size conventional battery. This is why a little PC680  
Odyssey can start a full size car. What isn't apparent to most people  
though is that you can't get something for nothing. A smaller battery  
has less capacity so if the charging system quits in a vehicle  
equipped with one of those tiny batteries they would be lucky to get  
to the next interstate exit before the car comes to a halt. You also  
can't count on any "sealed" battery to never vent gas into the  
interior where as the proper battery with the vent hose connection  
can't. As a bonus, the vented battery will last longer provided you  
think about topping off the cells with distilled water. Also, the  
professor who is the advisor for the race team says that Optimas are  
inappropriate for any application where they will be subject to a  
constant overcharge such as in an automotive electrical system. I  
can't remember the exact reason but I defer to him on this point.

Roy Wendell
erwendell at mac.com
Too many type 44 tq
A pair of MR2s