For those with a Coach Battery - EVC and others, I found this on the Yahoo Sprinter list yesterday. There is some Sprinter specific stuff, but the overall information should be very useful when deciding what sort of batteries to get.
Dave Richoux
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( Posted by: "Ken Slaughter" kenslaughter@... )
There are two
primary flavors of batteries (for our purposes here), sealed (SLA -
sealed lead acid) and flooded (FLA - flooded lead acid). Both are lead
acid batteries and have the same chemistry. The Odyssey batteries are
Sealed Lead Acid, and use the same liquid battery acid (electrolyte)
as the traditional wet cell, except that the electrolyte is absorbed
into glass mats (similar to fiberglass), so it doesn't slosh around
like in a wet cell battery. They are called AGM, for the Absorbed
Glass Mat construction. They are "dry" by design, only insofar as they
don't have free liquid sloshing around that can leak. AGM batteries,
even if broken open, will not leak. (well, they will, if you leave a
broken AGM battery laying there long enough. I guess "seep", maybe
"ooze" is a better word than leak).
The sealed, maintenance-free batteries, often marketed as "marine"
batteries, are merely traditional wet cell batteries that are sealed
and vented much like AGM batteries. However, with the cheaper
maintenance-free batteries, you can still add water if necessary (tho
sometimes how to get the caps off isn't readily apparent). Usually
you'll never need to add water, unless you have overcharged them and
they have, in fact, boiled over, outgassed and leaked. Some of the
maintenance-free batteries, like the ones marketed as "marine deep
cycle" like the Everstart Maxx marine batteries at Wal Mart, are
hybrid batteries, basically a cranking battery with slightly thicker
plates that will withstand deeper discharges than a cranking battery.
They aren't deep cycle batteries by a long shot. They are deep cycle
for starting a boat motor, and for use with a trolling motor. That's
what marine deep cycle means, it means a trolling motor battery, and
is designed to be drawn down and cycled in the same manner than a
trolling motor draws on it.
The design life of AGM batteries is indeed 8-10 year, but that's only
if they are properly taken care of, meaning not discharged below 50%
very often at all, and when they are recharged they are fully
recharged with the proper voltage. If you discharge too deeply and
then don't fully recharge them, the lifespan is dramatically reduced.
Like, from 8-10 year down to anywhere from 1-3 years.
Do keep in mind that if you want to charge an AGM house bank battery
with the same alternator that you charge your cranking battery, the
two batteries must be the same type, as in the cranking battery must
be an AGM battery, too, and not a standard cranking battery (sealed,
maintenance-free or traditional wet cell battery). AGM's and regular
cranking batteries (like the OEM Sprinter battery) require different
charging parameters, and a single alternator won't do that. Cranking
batteries require a variable, lower voltage (13.2-13.8), but a
relatively constant amps, while AGM's require a higher, constant
voltage (14.2-14.4), and the amps can be wildly variable. When you try
to charge AGM's with the vehicle's alternator, the AGM's will receive
the same low voltage and low amps that the cranking battery will get,
and the result is the AGM's will never be fully charged.
AGM's aren't like traditional batteries in the sense that with regular
batteries, you can charge them up fully at a lower voltage, it just
might take them a long time to get charged. With AGM's, if you try to
charge them at a voltage that is lower than 14.2, it doesn't matter
how long you leave them on the charger or alternator, they'll never
get fully charged. At best you'll get them to about 80% charged. And
chronic undercharging is the surest way to kill a battery before it's
time.
When you charge an AGM at, say, 13.6 volts, as the battery charges up
the internal resistance will match that of the charging voltage, and
when the internal voltage reaches 13.6 volts, and the charging voltage
is 13.6 volts, there ya go, charging stops, usually at around 80%, and
it won't charge beyond that, regardless of how long you pump 13.6
volts at it.
Even at that, the vehicle's alternator will throw a variable voltage
at the battery, not a constant 13.6 (or whatever) because the cranking
battery needs a constant amperage, not constant voltage,yet AGM's are
the opposite in that they need constant volts, variable amps.
Optima batteries are a hybrid, but are more like an AGM battery than
they are a "marine" or other battery type. They are true deep cycle
batteries, but are on the lower end of the deep cycle battery scale.
In the mid and upper range are the AGM (and gel) batteries from makers
like Odyssey (hardly the best battery you can buy, however), Deka, a
few others. And on the higher end of mid and upper range of consumer
AGM batteries you'll find Concord Lifeline and Discover Energy
batteries. The difference between the four brands I mention here are
small, and mainly related to specific applications, with Deka and
Odyssey being on one level and Concord and Discover Energy being
slightly above the other two. There are several differences, but the
primary one being the amount of amps you can pump into the different
batteries. Concord and Discover will take as many amps as you can pump
into them, up to 400% of the battery bank capacity, whereas Deka and
Odyssey will max out somewhere between 50% and 100% of capacity. Few
people will have the battery cables large enough to pump 400% of
battery capacity into a Concord. Imagine a 400 amp hour bank, and
trying to find a charger and telephone pole-sized battery cables that
can handle 1600 amps and 14.4 volts. That would be fun. :)
Just keep in mind that if you want to charge an AGM house battery with
the Sprinter's alternator, you really and truly do need an AGM
starting battery, in order to get the same voltage to both batteries.
Also keep in mind that AGM batteries don't perform very well at temps
below zero, so the cranking amps may be a little low at those times.
If you have different cranking and house bank batteries, this may be a
viable option.
I haven't talked with them, yet, but I plan to. They apparently have a
proven system with a tandem regulator for the Sprinter's Bosch
alternator that delivers different charging voltages to the house bank
and the cranking battery. Only thing I need to find out is how many
amps it can divert to the house bank, as it would be a shame to have a
150 amp alternator that only delivers the standard 30 or so amps of
charge to the batteries. It ain't cheap, but compared to the cost of 2
or 4 high end AGM's, it's pretty cheap if it'll keep them fully and
properly charged.
