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Old 18-03-2024, 02:00   #1
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AGM Maximum Discharge rate, Dead Giants

I run 4 * 140ah Giant batteries in parallel, and after 18 months they are dead.


I am wondering if my large inverter is the culprit, drawing up to 200 amps, i.e. 50 amps per battery when cooking electrically.



There is lots of talk about charging rates and minimum discharges and voltages, but not on current draw. Maximum for the batteries is 1200 amps each(!) but that is just for 5 seconds starting an engine.



Thoughts?
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Old 18-03-2024, 05:28   #2
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Re: AGM Maximum Discharge rate, Dead Giants

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Originally Posted by aberglas View Post
I run 4 * 140ah Giant batteries in parallel, and after 18 months they are dead.

I am wondering if my large inverter is the culprit, drawing up to 200 amps, i.e. 50 amps per battery when cooking electrically.

You're powering an electric cooktop with the inverter? Or long periods of convection oven/air fryer?

If so, maybe it's not exactly the inverter being the problem... more like the cooking.

We can do short bursts of microwave/oven/fryer, but don't power our electric cooktop (or water heater, or aircons) with the inverter.

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Old 18-03-2024, 06:28   #3
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Re: AGM Maximum Discharge rate, Dead Giants

I do not have any experience with the Giant brand of batteries, but in general, an AGM battery should have no trouble with a discharge rate of 0.3C. It’s what they are good at.

BUT.. If you draw 200 A for an hour to cook lunch, and 200 A for an hour to cook dinner from a 560 A-hr bank, and then do not recharge until tomorrow morning… that’s abuse.

Why your batteries died young we can not say, we know nothing about your system or useage. Sometimes a battery bank dies because of a problem with one of the batteries. But far more common is because they are mistreated. With AGM batteries in particular, the most common form of abuse is not bringing them up to full charge.
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Old 18-03-2024, 07:22   #4
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Re: AGM Maximum Discharge rate, Dead Giants

How are you charging them? How often, and how do you determine they are full when you stop charging?

If you now need to replace, get Lithium. The 200A load would not be an issue, and neither would irregular charging which is s likely the cause of AGM failure.
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Old 18-03-2024, 09:12   #5
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Re: AGM Maximum Discharge rate, Dead Giants

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If you now need to replace, get Lithium. The 200A load would not be an issue, and neither would irregular charging which is s likely the cause of AGM failure.
The only issue I have with this recommendation is someone who kills a lead battery bank through inattention or ignorance is quite likely to do the same to a lithium bank, with a much higher financial penalty.
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Old 18-03-2024, 14:44   #6
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Re: AGM Maximum Discharge rate, Dead Giants

Obviously we do not discharge below 50% total.


Cooking is actually very light in total power, because it does not go on for very long. Fridge uses more power over 24 hrs. Biggest cooking use is boiling water, I have bought a low power kettle, same energy usage but slower.



But it is the surge that I am wondering about. But AGMs are supposed to handle that.
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Old 18-03-2024, 14:45   #7
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Re: AGM Maximum Discharge rate, Dead Giants

Many lithium battery internal controllers will not tolerate a high drain. And you are not supposed to add up the max current if they are in parallel.
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Old 18-03-2024, 14:56   #8
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Re: AGM Maximum Discharge rate, Dead Giants

Quote:
Originally Posted by aberglas View Post
I run 4 * 140ah Giant batteries in parallel, and after 18 months they are dead.


I am wondering if my large inverter is the culprit, drawing up to 200 amps, i.e. 50 amps per battery when cooking electrically.



There is lots of talk about charging rates and minimum discharges and voltages, but not on current draw. Maximum for the batteries is 1200 amps each(!) but that is just for 5 seconds starting an engine.



Thoughts?
5 year pro rata warranty.https://giantpower.com.au/battery/gi...cycle-battery/

starting engine is 200-300A max. only if you have 1-2000 HP engine
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Old 18-03-2024, 15:49   #9
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Re: AGM Maximum Discharge rate, Dead Giants

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The only issue I have with this recommendation is someone who kills a lead battery bank through inattention or ignorance is quite likely to do the same to a lithium bank, with a much higher financial penalty.
Most of the reason to switch to Lithium is that if installed properly they don't require attention. They don't require being fully charged. They are not damaged by discharging too deeply (assuming BMS setup properly), and they are not damaged by PSOC, or by just ignoring them. Just forget about them and let them do their thing.

The OP did not answer how he was charging, or how it was determined they were fully charged everyday. The most common cause of early failure is not fully charging, and just assuming that solar is going to do that. AGM's without using a generator to charge is very difficult to fully charge, and early failure is the result.

You absolute CAN add up the current rating when putting LFP in parallel. You will want to derate it somewhat for any imbalance that might occur, but 4 LFP individually good for 100A will certainly be ok for 300A in parallel. And, it isn't difficult to find LFP batteries good for 250A, example the 400Ah LiTime. 2 of those would be considerably more power than you have now, lighter, more reliable, longer life, and together good for 400+ Amps.

I am only suggesting this because the AGM reportable are dead. It would be very ignorant to not seriously consider LFP at this point.
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Old 18-03-2024, 16:11   #10
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Re: AGM Maximum Discharge rate, Dead Giants

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Obviously we do not discharge below 50% total.
You very well might not, but people do sometimes because they do not understand how a battery monitor actually works, and when it does not. And trust me, when you work with boat owners, it is ALWAYS a bad idea to assume they know what they are doing. I am sure I sometimes insult the intelligence of customers when I ask them if they understand a specific issue, but the damage done by making the assumption they know can be far worse!

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Originally Posted by aberglas View Post
But it is the surge that I am wondering about. But AGMs are supposed to handle that.
AGMís can handle the power surge you describe just fine. That was your original question. If you want to know the real reason they failed you have to supply a LOT more data about your system and how you manage it.
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