Thanks for your response.
I found a couple of interesting points of info you and others running AGM batteries may be interested in:
First from Justin Gobar at Lifeline:
http://www.morganscloud.com/2010/08/10/agm-battery-test-2/
"Justin Gobar at Lifeline, who provided us with new batteries, is advising us on how to care for them. Put broadly, there are four ways that will yield different lifetimes based on daily 50% deep cycles:
Fully charge after each discharge. (We understand that is not feasible [in our case].) Estimated life: 6-9 Years.
Fully Recharge at least once a week and equalize once a month. Estimated life: 4-6 Years.
Only recharge to 85% and equalize once a month. Estimated life: 2-4 years.
Only charge to 85% and never equalize. Estimated life: 1 year."
Next from the Odyssey:
http://www.odysseybattery.com/documents/US-ODY-TM-001_0411_000.pdf (page 11)
"The true dual purpose design of ODYSSEY batteries
is reflected in the cycle life results shown in the graph
below. The two ODYSSEY 65-PC1750 battery samples
were discharged at 25A (the reserve capacity rate) for 108
minutes (80% of 135 minutes, which is the 100% rate for this
battery), rested for an hour then charged for 5 hours at 14.7V
with a 50A current limit. Since five hours are not sufficient to
charge them completely, both batteries were given 20-hour
charges every ten cycles. Sample 1 cycled 581 times and
Sample 2 lasted 544 cycles before reaching end of life.
So it sounds like if you aren't charging your batteries elsewhere at least 10% of the time you are probably running them chronically low. Also if you are running them chronically low you are probably shortening their life, possibly drastically.
How many people here are checking their batteries for charge level?
How many are methodically recharging off the grid/solar at regular intervals.
I think in view of the post to which I am responding here and this additional information my money would be better spent on a good AC step charger used regularly on my RV. I do typically drive 4-8 hours a day when traveling but stop or drive minimally for several days as well.
Note different manufacturers recommend differing charging regimens and different batteries have different lifetime characteristics. Regardless these AGM batteries do require attention if one wants to get the best out of them.
Mike
You can put the solenoid on a manual switch, perhaps an illuminated one and decide when to parallel the batteries for charging.
About the charging voltages and fully charging batteries, here is my opinion:
Fully charging any Lead acid battery via alternator is a futile enterprise requiring hundreds of miles of driving, regardless of charging voltages, even prime ones.
By all means utilize the alternator with adequate cabling to take advantage of this power source, but to reach a true 100% state of charge, solar, or a grid powered charger after an outing is the only effective means of accomplishing the task, as going from 95% to 100% can take 12 hours, if one cares to take specific gravity readings and has a new battery fully charged specific gravity baseline to compare it with. Most 'automatic' chargers stop in the 95 to 97% charged range.
Any anybody who thinks an hour or 2 of driving completely charges a depleted auxiliary battery is smoking crack. Idling to fully recharge is even more futile, wasteful, and only occurs in the combo meth/crack smoker's reality.
