Mixing AGM with Wet Cell, different banks..

I have a dead starting battery, 4D wet cell. My house bank is three 8D's also wet cells. I have an inverter, smart charger, combiner. The 8D house batteries are in good shape, new in 2016 and don't need replacing. Eventually I would like to upgrade all to AGM's. If I replace the dead wet cell with an AGM can a smart charger / combiner handle two different types? Does that depend on the charger/combiner?

You would have to check and see if your charger can do 2 different battery types. I know mine does not allow 2 different types. I would not mix them if the charger does not specifically say that it can do 2 types. Another thing you could do is add a small charger dedicated to just the start battery until you change out your house bank. For a start battery you should not need much charging, maybe a 10 or 15 amp charger. Then when you change out the house bank you could go back to using one charger.

AGMs and FLAs (flooded cell lead acid) batteries have close enough charging characteristics that you can use them combined on the same shore power charger. Others may disagree. But when AGMs first came out (yes I was boating at that time), the manufacturer's said it was ok. Now maybe.....


David

firstbase said:

I have a dead starting battery, 4D wet cell. My house bank is three 8D's also wet cells. I have an inverter, smart charger, combiner. The 8D house batteries are in good shape, new in 2016 and don't need replacing. Eventually I would like to upgrade all to AGM's. If I replace the dead wet cell with an AGM can a smart charger / combiner handle two different types? Does that depend on the charger/combiner?

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I used an AGM house bank with wet cell LA starter bank for over a decade with no issues. Same charging profile for both. Balmar MC 6xx smart regulator.

Delfin said:

I used an AGM house bank with wet cell LA starter bank for over a decade with no issues. Same charging profile for both. Balmar MC 6xx smart regulator.

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I have a similar setup, a pair of AGM house batteries with wet cell engine and electronics battery. My charger charges both so far without any issues with my battery switch in the all position when the boat sits stored on the shed for a period of time.

Thanks guys, good to hear. I will ask the electrician I have doing some work as well as an audit/survey for me. Replacing my old combiner, adding some GFCI's, etc. Electricity is NOT one of my better things at this point.

"220v...221v....whatever it takes."
Michael Keaton, Mr. Mom - 1983
Firstbase, Black Eyed Susan, 2019

I think most agm have lower charge voltage than flooded, so if you set your charger to agm, the agm will be fine and the flooded will just charge a little slower.

Batts don't know what they are tied to. Only know charge volts and amps and discharge volts and amps. If all is ok for both batt flavors, then it is ok.

AGM vs Flooded Lead Acid (FLA)

AGM batteries ---Absorbed Glass Mat Batteries --- need a little more TLC than FLA batteries (Flooded Lead Acid batteries) & they have different charge acceptance, different internal resistance, different internal self discharge rate, & a few other things. They are different. And there are different type of AMG's (spiral, flat plate, etc.) out there as well, but more on that another day.

Also, AGM batteries are not happy if they get to hot. Max core temp for any extended period is not recommended to exceeded 125 degrees F.


In the new cars with the "stop start technology", a lot of them moved the AGM starting battery to the trunk or under the back seat, etc. - why ? - to keep it in a cooler environment than the hot under hood environment. This helps the battery last longer.

To keep the core temp under control please follow this guide line.

AGM batteries are not to be charged above 14.5 volts for any extended time period.

Also not recommended to be charged at a higher rate than 20 amp rate for any extended periods.

Also, recommend that once AGM's reach full charge, to turn the charger off or have a smart charger that reduces the charging to almost zero amps when the AGM battery is 100% full.... which is not as necessary when you have FLA batteries.

Why ? - because AGM's don't have the flooded liquid electrolyte to dissipate the core heat. As You can over heat the core of the AGM battery more easily that FLA ( Flooded Lead Acid) batteries. This can damage the battery.

(FLA) Flooded Lead Acid batteries on the other hand are very flexible in accepting how you charge them -- so as long as not in same bank, just set up the charger & charging relay for the AGM's voltages & the lead acid batteries will be OK - just charge a little slower, so a bit more time in reaching full charge.

NOTE: This would be if there is a charging relay or battery combined that combines them only when charging, but importantly not being combined when being used & especially not when they are just sitting & not wired in parallel with no disconnect between them when boat is shut down, just sitting & all is off.

I think you were using the AGM for starting & not for the house bank - so for that you should be ok as should be separate circuits.

If you have them all wired in parallel, like in a house battery bank, don't mix, as Manufactures of AGM batteries prefer for Maximum battery life to have the bank be all the same type of batteries -- either all AGM's or all Flooded.

So, Not recommended to mix them in the same bank.

One more thing to mention; I have a device called a Battery to Battery charger. It is a battery powered charger that runs off my house flooded 12-v LA batteries & I use it to charge my 24-v AGM batteries for the thruster & can be set up for AGM's & yet be powered by FLA. -- works very well & you might want to look into one of these.

Good luck with your project.

Alfa Mike

firstbase said:

I have a dead starting battery, 4D wet cell. ... Eventually I would like to upgrade all to AGM's. If I replace the dead wet cell with an AGM can a smart charger / combiner handle two different types? Does that depend on the charger/combiner?

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I did exactly that, as we upgraded battery banks over time. First replaced a bank of 3x FLAs with 3X AGMs. Three years later, replaced the second bank of 3x FLAs with AGMs, and also replaced the third bank (a single smaller FLA) with AGM.

Useful in our situation that a) our charger manual said to use FLA setting for AGMs, and b) I happened to choose AGMs that coincided with voltages of that charging profile. Latter was a happy coincidence, 'cause at the time I didn't realize some AGMs want significantly different charging voltages than others, didn't realize various manufacturers make their own recommendations.

That charger happens to provide 14.7V bulk/absorption charges and 13.5V float. The Odyssey AGMs I chose want between 14.1-14.7V bulk/absorption, and between 13.5-13.8V float. And presumably the non-descript FLAs that were on the boat when we got it were OK with those charges, too.

Yay. All good. That first bank lasted 11-12 seasons, second entering 11th season now, I think.

BUT... had I chosen Lifeline AGMs back then, they want only 14.3V (plus/minus .1V) bulk/absorption and 13.3V (plus/minus .1V) float... so they would potentially have been being overcharged on that charger.

Newer chargers offer more pre-set charging profiles, and some let you name that tune yourself. In that case, I could have dialed in whatever voltages the batteries wanted...

OTOH, multi-bank chargers generally use the same voltage settings for all banks... so there's only so much flexibility... possibly best addressed during your "shopping" phase as you look at which AGMs to choose.

Note also, some AGM makers recommend really high charge rates. Odyssey, for example wants a minimum of 40A for a single 100Ah PC-2150 (Group 31), so that's a .4C minimum. Hard to do that with banks of multiple batteries... I didn't notice (or maybe can't measure) any bad effects on ours with only a single 40A charger on two 300Ah banks and one 68Ah bank for several years, though...

-Chris

alfamike said:

Also not recommended to be charged at a higher rate than 20 amp rate for any extended periods.

Also, recommend that once AGM's reach full charge, to turn the charger off or have a smart charger that reduces the charging to almost zero amps when the AGM battery is 100% full.... which is not as necessary when you have FLA batteries.


Alfa Mike

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Consult the battery manufacturer's data on charging. For at least Lifeline AGM's (and several others) this information is incorrect.

Great information here.

BUT

Call the manufacture of your charger to confirm all the above.

FWIW, I had a mix of AGM and FLA batteries on my boat for a number of years. Not ideal, but not huge issue. Unless you go to a high quality DC-DC charger that allows for different charge profiles, I would just look at the manufacturers specs and come up with the best compromise.