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Old 04-18-2015, 03:17 PM   #1
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Mixing AGM and flooded batteries?

my coach batteries are trojan wet cells. my chassis battery is dead now. i am in a position to decide which battery to get - a deka 908d to replace the same chassis battery for $200, or a deka agm for $180. cca is the same.

i have an intention to upgrade the coach batteries to lithium in next few years, so getting an agm starting battery may make sense for future that there will be no gassing in the battery bay. but, all the schools have taught me not to mix different types of batteries (though i think they are not in the same circuit). i talked to xantrex cs about the settings on interface charger/inverter 20d, they told me to select wet cell warm or cold for agm. i understood shore power and solar charging will not cause a problem for agm.

now is the question - which one to get?
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Old 04-18-2015, 03:30 PM   #2
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I have AGM coach batteries, and sealed wet cell chassis batteries. I always thought that AGM didn't have the CCA needed for starting bats. But if the CCA is the same, I guess they're OK. I'm surprised the AGM are cheaper. But I wouldn't mix the two types in the same bank no matter what.
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Old 04-18-2015, 05:17 PM   #3
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yea it was inserted into my mind that the agm would cost an arm and a leg to get. when i got to the store, they showed me more than 10 of deka agm batts. to my surprise, the agm's cca was even higher than flooded's - 1450 vs 1400. don't know how they got those agms at that price, but i bought one daring to gamble
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Old 04-18-2015, 11:52 PM   #4
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Is that a 8D AGM for $200?
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Old 04-19-2015, 04:12 AM   #5
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Never mix AGM with wet batteries in the same Bank. Mixing the two together will reduce the battery life of both.

AGM for coach and Wet for engine is okay.
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Old 04-19-2015, 09:10 AM   #6
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Is that a 8D AGM for $200?
yeah, it's 8a8d. sounds like too good to be true. measured voltage is 12.82v
now.
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Old 04-19-2015, 09:12 AM   #7
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Never mix AGM with wet batteries in the same Bank. Mixing the two together will reduce the battery life of both.

AGM for coach and Wet for engine is okay.
mine is opposite - agm for engine and wet for coach. will it cause problem?
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Old 04-19-2015, 09:17 AM   #8
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Actually you can run either as long as you run matched batteries in a set. The one issue you may find is your chassis charging system may be too hot for AGM batteries and shorten their life. If your alt puts out over 14.2 you will damage AGM batteries.
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Old 04-19-2015, 09:43 AM   #9
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Actually you can run either as long as you run matched batteries in a set. The one issue you may find is your chassis charging system may be too hot for AGM batteries and shorten their life. If your alt puts out over 14.2 you will damage AGM batteries.
if both chassis and coach batts were agm, wouldn't the charging system do the same thing?
to my understanding, alternator's electricity does not go through charger/inverter, it goes to batteries directly. there are a lot of cc owners using agm, (not counting non-cc mhs). if they have no issues on alt charging, should i be worry about it?
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Old 04-19-2015, 09:54 AM   #10
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Yes. Life line says it will just shorten the batteries life. At 70 degrees, life line says float at 13.5, lead acid 14.2.
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Old 04-19-2015, 10:24 AM   #11
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In a lab you can measure a difference in lifetime due to mixing battery types on the same charger, or even mixing different battery ages. But in practice I see little difference as long as the entire system is in good shape and the charger is 'smart" about managing charge rates and float.

My own examples: I have two Harris maintenance free flooded cells on the chassis circuit and 4 Trojan AGMs for the house. Both get charged by the Xantrex inverter when on shore power, and the alternator when driving. Both sets of batteries are now 7 years old and still humming along. AGMs don't have the amp-hour capacity they used to, but still usable. And my Xantrex RV2500 inverter doesn't even have a selectable charge rate for AGM - it treats all batteries the same, no matter what. Batteries float at 13.6, period.

But, "your mileage may vary".
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Old 04-19-2015, 10:37 AM   #12
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You can get an external, adjustable voltage regulator for your alternator, to cure the issue. My Balmar , is programmable.
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Old 04-19-2015, 10:47 AM   #13
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You can get an external, adjustable voltage regulator for your alternator, to cure the issue. My Balmar , is programmable.
didn't know it is available. MC-614 voltage regulator sounds like a good one.
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Old 04-19-2015, 11:05 AM   #14
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I think Sterling makes a well reviews one also.
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