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Old 13-04-2015, 14:05   #1
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Mixing AGM and Lead Acid batteries

Yes, not a good idea in general, but...

Here is my situation:

Got a Duffy electric boat.
8 Golf Cart battereies, Trojans T-105.
Works good last a long time.
The bank is wired in series and parallel to 48 Volts.
They are all 4+ years old.
Holding up good and I never go below 65-70%, about 3-4 hrs running time.
A few weeks ago I noticed a big voltage drop after running the usual 3 hrs.
Started trouble shooting the basics, loose terminals, corrosion, etc.
Found one of the batteries low on voltage when isolated from the rest of the bank.
Measured the specific gravity in all 24 cells after running, and down to a theoretical 70%.
The range was 12.10 to 12.40, except 1 cell in the culprit battery which was 11.00.
Okay, dead cell and it dragged the rest down.
The boat kept running okay however. It perhaps less spunk than before.
Can't put a new 6 Volt Golf Cart in the bank however, it would not last long as it would overcharge every time.
Went to different battery place to look for a used 6 volt Lead Acid to somehow match the rest of the batteries.
No cigar.
Until today, found a 6 volt AGM in good shape, $40.00.
Installed it and life is good.
Curious how long it will last being 1 AGM with 7 Lead acid batteries?
The charger is factory set for flooded lead acid batteries and will initially go to 60+ Volts, or 7.5 for each battery before it tapers off.
Just buying time here:
The 7 lead acid batteries are doing good and probably have 2 years left.
To do it 100% right I should have bought a whole new bank for $1000, but this is not the space shuttle and the $1000 can wait, $40 was about right for buying time.
Any thoughts on how long that lonely AGM should last?
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Old 13-04-2015, 17:11   #2
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Re: Mixing AGM and Lead Acid batteries

First, AGM's are lead-acid batteries, too. Just as are gelled batteries.

Not sure why you thought that a new T-105 or similar flooded golf-cart battery would be "overcharged every time". Why? Trojan calls for charging voltages between 14.8 and 15.0 for the T-105s in 12VDC configurations, or 7.4-7.5VDC per battery.

IMHO, that would have been your best bet.

The AGMs generally require a somewhat lower absorption voltage, on the order of 7.2-7.3VDC. However, some of them can tolerate higher charging voltages pretty well.

What you have is an interesting test project!

Let us know how it works out.

Bill
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Old 13-04-2015, 18:45   #3
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Re: Mixing AGM and Lead Acid batteries

Quote:
.
Let us know how it works out.

Bill
Not good.
Almost had a fire today.
One of the terminals on the battery next to the AGN melted and came loose from the battery.
It smelled burned for awhile and power was way down going up the river.
Did not investigate until I was docked.
The AGM was rather hot once I started investigating.
No idea what went wrong, but it did.
Tomorrow going to Costco, looking for best deal on 8 new batteries.
Moral of the story?
I am stupid (
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Old 14-04-2015, 11:42   #4
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Re: Mixing AGM and Lead Acid batteries

Found the problem.
The melt-down was not because I mixed batteries but rather because I left a
Cable connector on the battery loose: While shuffling the batteries around I put a cable on a battery post and started the lug-nut, just one three so I would remember where it went and planned to torque it down later when all the batteries was in place and connected.
Then I forgot.
The very loose connection built up heat to the point where it melted the stud right of the battery.
Entirely my bad and my sloppiness....
Took the damaged battery (not the AGM) back to the battery place.
(East Coast Batteries in Fort Lauderdale, highly recommended)
They had another AGM in good shape for $40 and with the two core trade-ins at $10 each, today's battery cost me $20. 2 new Cable connectors for $7 each and I am good to go again. Now charging the whole bank and will do a test-ride in an
hours. Should be good to go.
Moral of the story, I am stupid and should use a check-list...
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Old 14-04-2015, 11:49   #5
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Be careful out there....

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Old 14-04-2015, 11:57   #6
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Re: Mixing AGM and Lead Acid batteries

When in doubt leave everything disconnected. A shorted bat or a bad wire can burn a boat.

b.
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Old 14-04-2015, 12:28   #7
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Re: Mixing AGM and Lead Acid batteries

Quote:
Originally Posted by CSY Man View Post
Not good.
Almost had a fire today.
One of the terminals on the battery next to the AGN melted and came loose from the battery. . .
(
As stated by other members - AGM's are lead-acid batteries the difference being in that the liquid acid is confined by sheets of fiberglass between the plates rather than having nothing between the plates except the acid. This helps keep the acid in contact with the plates better especially when the battery is not mounted in an "up" orientation.

Since AGM's are in fact liquid lead acid batteries - - the acid level can decrease with age and use. Normally the AGM's are "sealed" which means that the acid is not easily accessible and the battery case has a vent valve to allow excess pressure to escape should you over-volt or over-charge the battery.

AGM's, in my experience of over a dozen years of using them, are more sensitive to each "step" in the re-charging process. So I use top of the line "smart" charging regulators to keep my AGM's within the recommended parameters.

However, overcharging and other stressful use will cause the "liquid acid" in an AGM to heat up and vent through the case valves. Over the years you can end up with a battery with low acid levels in the cells. This will most probably result in cell failures and thermal run-away events that could lead to a smoking battery or even a battery fire.

After a particularly nasty failure of one of my AGM's I took it apart and found out that you can get access to the liquid acid compartments within the battery. And the cells that failed were ones with obviously very low liquid acid levels. So here is my conclusion - in order to get the maximum possible life out of an AGM you do need to "check" the acid levels occasionally and replenish the water if the level is low. On my AGM's the "valve" on the top of the battery was indeed capable of being "unscrewed" allowing access to the inside of the cell. Checking and refilling the water level would most probably do two things, help keep thermal run-aways to a minimum and help extend the life of the AGM battery to its maximum possible. Considering the cost of the AGM versus ordinary liquid lead acid batteries, that could make the AGM's cost effective.
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Old 14-04-2015, 12:28   #8
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Re: Mixing AGM and Lead Acid batteries

Quote:
.When in doubt leave everything disconnected
Yup, agreed.
I was not in doubt however but rather cocky and in a hurry to go cruising on the local canals and the River in Fort Lauderdale.
Having extensive experience with installing and hooking up house banks and start batteries from various sailboats I have owned, and other boats I have managed, the above was fairly routine...

Now, another decision to make:
East Coast Batteries, the folks I got my recent AGM batteries from had a total of 8 before I bought two of them.
In other words, they have 6 more and my bank on the Duffy consists of 8 batteries.
With my Leas Acid batteries being 4+ years old, I may consider getting the remaining 6 AGMs for $30 a piece after the $10 core charge for my old 'uns.
(The used AGMs came from some RV guy that wanted a whole new bank)

Question: How long does AGMs last?
Do they stand up to 100-110 F degree heat in the summer?

I have had Deka Golf Cart batteries last me 6 years as a house bank on the sailboat.
How long will AGM last?
(Not sure yet, but my built in charger on the Duffy boat may have a switch for AGMs. if not, will the AGMs take the initial charge of 7.5 volts in the long run?)
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Old 14-04-2015, 12:41   #9
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Re: Mixing AGM and Lead Acid batteries

Osirissail:

Just now saw yer response after I posted the last message.

Cool, will look and see if I have a valve that can be opened.
Will get the details on my new AGMs in case we have the same brand/type.

One of my neighbors is a Deka distributor and I get Lead Acid Golf Cart batteries
For "Friends and Family" price, about $90 each.
Have used Dekas in the past and again, they can last 6 years, good stuff.

I thought, perhaps not true, that Costco are selling their Golf Cart batteries for $65 or so.
Did not make it there today as I found the Self Induced Problem and the fix cost me $20....
In the long run, I should get a new bank and be worry free for the next 5-6 years.
The Duffy boat is a toy used locally, with full towing insurance, so I don't have to get the best and most expensive bank for an around the world cruise, just looking for a few more years without headaches...
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Old 14-04-2015, 12:47   #10
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Re: Mixing AGM and Lead Acid batteries

Quote:
Originally Posted by osirissail View Post
As stated by other members - AGM's are lead-acid batteries the difference being in that the liquid acid is confined by sheets of fiberglass between the plates rather than having nothing between the plates except the acid. This helps keep the acid in contact with the plates better especially when the battery is not mounted in an "up" orientation.

Since AGM's are in fact liquid lead acid batteries - - the acid level can decrease with age and use. Normally the AGM's are "sealed" which means that the acid is not easily accessible and the battery case has a vent valve to allow excess pressure to escape should you over-volt or over-charge the battery.

AGM's, in my experience of over a dozen years of using them, are more sensitive to each "step" in the re-charging process. So I use top of the line "smart" charging regulators to keep my AGM's within the recommended parameters.

However, overcharging and other stressful use will cause the "liquid acid" in an AGM to heat up and vent through the case valves. Over the years you can end up with a battery with low acid levels in the cells. This will most probably result in cell failures and thermal run-away events that could lead to a smoking battery or even a battery fire.

After a particularly nasty failure of one of my AGM's I took it apart and found out that you can get access to the liquid acid compartments within the battery. And the cells that failed were ones with obviously very low liquid acid levels. So here is my conclusion - in order to get the maximum possible life out of an AGM you do need to "check" the acid levels occasionally and replenish the water if the level is low. On my AGM's the "valve" on the top of the battery was indeed capable of being "unscrewed" allowing access to the inside of the cell. Checking and refilling the water level would most probably do two things, help keep thermal run-aways to a minimum and help extend the life of the AGM battery to its maximum possible. Considering the cost of the AGM versus ordinary liquid lead acid batteries, that could make the AGM's cost effective.

Absolutely DO NOT open up AGM batteries to 'check the electrolyte level'. First off, if you have good ones they come with at least a 5-year, sometimes 10-year warranty. Tampering with them in such a fashion will void this warranty. Second, AGM batteries are pressurised in the factory. The contents are under pressure, and unscrewing or otherwise removing the caps will release this pressure with, at best, bad consequences (preventing re-combination of gaseous water during charging. The high pressure favours re-combination) and at worst blowing sulphuric acid all over the place and blinding you.
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Old 14-04-2015, 13:12   #11
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Re: Mixing AGM and Lead Acid batteries

Ouch, perhaps not a good idea....
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Old 14-04-2015, 13:24   #12
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New (used) AGM

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Old 14-04-2015, 13:27   #13
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Old 14-04-2015, 13:38   #14
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Re: Mixing AGM and Lead Acid batteries

On one hand, I sympathise with you about trying to save money, BUT IMHO you have picked a route that is guaranteed to destroy all of your batteries sooner, rather than later.

Go buy another wet golf cart battery. THat's your best solution and yes, while not optimum, you choose a route that can't work for many reasons.
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Old 14-04-2015, 16:18   #15
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Re: Mixing AGM and Lead Acid batteries

Quote:
. On one hand, I sympathise with you about trying to save money, BUT IMHO you have picked a route that is guaranteed to destroy all of your batteries sooner, rather than later.

Go buy another wet golf cart battery. THat's your best solution and yes, while not optimum, you choose a route that can't work for many reasons.
Thx, appreciate all opinions.

The problem with buying another wet golf cart battery is that a new one will burn out in 90 days as it accepts a charge much better than the old ones in the same bank.
Or so the experts told me.

For now I am buying time and saving money.
Again, this is a toy boat with no serious cruising going on.

If a new bank is $800.00 with a life expetancy of 5 years, it comes to $13 per month.
If I spend $60 to get another year or two, I will use the savings to go out for a couple of nice dinners with the old lady and the old boat will run just as good with old or mixed batteries.
So yes, I am being cheap as there is no benefits to expensive right now.
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