dwh- I don't think the tech was reading from a script. I specifically asked if the valves only "Blow" at serious overcharge, he replied they are designed to release slowly at any overcharge causing premature drying. " Even at 14 volts" I asked, yes, he was adamant " any over voltage will produce a loss and premature drying, the degree will depend on the amount of overcharge".
Okay, assuming for the moment that he actually knows what he's talking about...
If what he says is true and the valve opens and allows the battery to vent at any voltage over 14v (temperature dependent of course) - then every single VRLA (flooded, AGM or Gel) engine CRANKING battery is drying out 99.9% of the time a vehicle is being driven, since the cranking battery only gets drawn down like .1 or .2 amp*hours when the vehicle is started and then is topped off in minutes.
After that, it just sits there being held at 14v+ in a hot environment for however long the vehicle is being driven. On my truck, it's 13.5v at idle, 14.5v at any RPM above idle.
(And while there might not be millions of deep cycle batteries running around Mojave in the summer, there ARE millions of VRLA cranking batteries running around everywhere else in the summer. I've seen it get to 111 in the shade - in BURBANK.)
(And since I can see the objection coming; that there is a difference between cranking and deep cycle - no, that doesn't wash. If they used a higher pressure valve in cranking batteries, there is no reason not to use the same valve in deep cycle batteries.)
I don't buy it.
That's basically saying the battery was *designed* to dry out.
Hell, if that were true, the wouldn't make, sell and *warranty* AGM engine cranking batteries - because they know they are all going to dry out, because they were *designed* that way.
Engineers might be stupid sometimes, but they aren't THAT stupid.
But then again...engineers don't always get to make the final call.
I do recall reading somewhere long ago that when they started adding platinum catalyst to VRLA batteries to reduce water loss from gassing, they had some problems with it. As I recall, it had something to do with new cells straight off the production line are not all perfectly equal, and one of the results of charging them, is that some gas a bit more than others, so they all end up equal. But adding the catalyst reduced the gassing to almost nothing, so new cells never did end up getting equalized.
I think they solved that by implementing a procedure to deliberately overcharge the battery at the factory, forcing the valve to open and the cells to equalize. This is why even though every manufacturer tells you to never do an equalize on a VRLA battery - they all do actually have a procedure to do it. They just won't tell dopey battery owners that there is a way to do it. Basically you need an adjustable regulated power supply and the top secret, burn before reading, voltage/time numbers from the factory.
But maybe some bright management type came up with the idea to lower the pressure threshold on the valve, to allow more gassing and a quicker equalizing of the new cells. Save the factory some work. Shave a few cents off the cost per unit. Give the stockholders a chubby with a little uptick in the quarterly report.
The downside to that would be an increased sensitivity to overvoltage. That *would* be stupid - especially in a cranking battery that pretty much always operates in a hot environment and at 14v+.
But that doesn't mean it didn't happen, because the upside would be a shorter battery life - let's say...an hour past the expiration of the warranty - which would result in long-term increased sales and give the stockholders serious wood.
Damn, that's almost as good as shutting down the US factory, tossing all the workers out into the street and getting some poor bastards in the third world to do the work for 2 bucks an hour (or two bucks a day, depending on where you setup your new factory). Definitely some stockholder wood there.
Corporations ARE inherently sociopathic structures, since nothing matters to stockholders except the bottom line, so it wouldn't surprise me a bit.
Let's look at your concern about the life of the expensive batteries...
Here's the life cycle graph from Lifeline:
So the question is: How far do you draw down your battery, and how many times do you do it?
If you draw down to 50%, then you're only looking at 1000 cycles. For a full-timer, that would be 3 years and then the battery is shot.
So, even if you reduced "dryout" to nothing. How long could you realistically expect the battery to live? You'd have to answer that, since you're the one who knows how you use it.
Since you are worried about premature drying out; how could you solve that?
You could use a DC-DC charger, which draws from the vehicle bus and converts that into a proper multi-stage charging profile WITH a proper float voltage. That would work fine if you had a single battery or a small bank - AND you drove enough to get all the way through the full bulk/absorb stages.
