AGM bateery capacity

laurieoz · Senior Member

AGM bateery capacity

Possum3 · Guru

Laurie you will need to check voltage with a voltmeter - Eight year old AGM Batteries would definitely be near the end of their life.

laurieoz · Senior Member

Possum3 wrote:
Laurie you will need to check voltage with a voltmeter - Eight year old AGM Batteries would definitely be near the end of their life.

Hi

I have had the batterys disconnected for 4 days

Still 12.83 Volts today

Can the voltage stay up but the capacity of the batterys drop?

Is testing the voltage at rest the only way to test the remaining capacity?

Laurie

-- Edited by laurieoz on Monday 1st of August 2022 08:42:48 PM

Whenarewethere · Guru

I have a 10 year old 85AH starter battery which I use for testing things & carefully look after it. Used it a few weeks ago to jump start an Audi 6 cylinder diesel, while at it I had my DC clamp meter connected. 344 amps to start the car.

But my own car's starter & auxiliary batteries I replace every 4 years, amortised over that period it hardly anything. Certainly not worth the wrath of the dragon if inconvenienced at the wrong time.

Rule of thumb lead acid batteries lose about 20% per year from date of manufacture, not the day you bought them. If treated well you will get a bit longer but the AH will be a lot less.

To test put a 20 hour load on them (10amps for 200AH) & test voltage & amps every hour & jot figures down on the back of an envelope.

The Travelling Dillberries · Guru

laurieoz wrote:
Possum3 wrote:
Laurie you will need to check voltage with a voltmeter - Eight year old AGM Batteries would definitely be near the end of their life.
Hi
I have had the batterys disconnected for 4 days
Still 12.83 Volts today
Can the voltage stay up but the capacity of the batterys drop?
Is testing the voltage at rest the only way to test the remaining capacity?
Laurie

-- Edited by laurieoz on Monday 1st of August 2022 06:56:28 PM

To answer your question, testing voltage only gives an indication that the battery may be ok, to be certain they have more life, take them to a battery house and have each one load tested.

Jaahn · Guru

laurieoz wrote:
I have two 100 amp AGM battery in parallel.
1. How do I determine the the capacity of the batterys
as they are 8 years old. Laurie

Hi Laurie smile

You could take them to a battery shop and they will test them with their black box. But as they are designed to sell batteries they will most likely say they are past it biggrin The electronic testers they now use do not properly test deep cycle batteries anyway.

If you wished to test them yourself then you need a load to use, say 5A like a car 60W headlight, some wire and clips, and a voltmeter. Measure the voltage at the start and clip the globe on and see how the voltage goes down over time.

A new fully charged 100 Ah battery should keep going at 5 A for 20 hrs in theory. However it would not be wise to run your old batteries right down too far as they might just give up. Just run them individually for an hour and see what the voltage is then. After a 10 min rest time compare that to the table below.

?u=https%3A%2F%2Ftse4.mm.bing.net%2Fth%3

Note that any serious load testing on an 8 year old battery might likely be the last gasp of their life.

Jaahn

-- Edited by Jaahn on Tuesday 2nd of August 2022 09:36:46 AM

laurieoz · Senior Member

Jaahn wrote:
laurieoz wrote:
I have two 100 amp AGM battery in parallel.
1. How do I determine the the capacity of the batterys
as they are 8 years old. Laurie
Hi Laurie
You could take them to a battery shop and they will test them with their black box. But as they are designed to sell batteries they will most likely say they are past it The electronic testers they now use do not properly test deep cycle batteries anyway.
If you wished to test them yourself then you need a load to use, say 5A like a car 60W headlight, some wire and clips, and a voltmeter. Measure the voltage at the start and clip the globe on and see how the voltage goes down over time.
A new fully charged 100 Ah battery should keep going at 5 A for 20 hrs in theory. However it would not be wise to run your old batteries right down too far as they might just give up. Just run them individually for an hour and see what the voltage is then. After a 10 min rest time compare that to the table below.

Note that any serious load testing on an 8 year old battery might likely be the last gasp of their life.
Jaahn

-- Edited by Jaahn on Tuesday 2nd of August 2022 09:36:46 AM

Thanks

Laurie

Mike Harding · Guru

There is an Australian standard devoted to determining the capacity of sealed lead acid batteries - to do such is not simple and involves constant current loads and temperature controlled environments.

Find a known load, perhaps a 12V light globe, fully charge the battery, connect the light globe and measure the time until the battery terminal voltage drops to 10.5 volts.

eg. with a 50W globe we'll say it draws 4A so if the battery supports it for six hours then it has a capacity of 24Ah.

Please understand this is not an accurate test but it will give you a good indication of what's happening. With a sealed lead acid battery there is no other way.

Unfortunately, at eight years of age, your batteries are probably stuffed :(

TimTim · Guru

laurieoz wrote:
I have two 100 amp AGM battery in parallel.
1. How do I determine the the capacity of the batterys
as they are 8 years old
Laurie

Im not sure if you have problems running things with your batteries but to test the capacity of numerous batteries I have I bought one of these.

https://www.ebay.com.au/itm/192890203381?hash=item2ce926ecf5:g:nTAAAOSwiahctD4g&amdata=enc%3AAQAHAAAA8DXh1jG3Io2DEztdCq1OUT2IX59ae4QjJ9HRmZO%2BJucnTNVnhr36Ybfh8xV%2BInZbfeAGIrnqxcp69KJ9eL5PrJijTAmunMbPj06Lny27JktuEZ2PUQ9ytJ7Z%2BeRgXrPHXzBDH0Q3lac7dC5fz43h9Ybk1ZaBNJA3JoBt28Xd4M9a2SBsNjEgVze6zUwX7s5EbaiyqEi05K1gY6OHh6mIUQyURYmFAkHUfz%2FkdO%2BihRcZzJpP2%2Bc3ETDKbScnnBL92MV6E%2F9UpaMKi8vVE3m9ZSbyx2fioP6uq990Akmh%2F1kPSCcDDXLABJOe0i4KkOa8ug%3D%3D%7Ctkp%3ABFBM-O7a_8pg

It is recommended that you change the connector cable to a decent size and fit some terminal lugs of instead of the pathetic alligator clips but that is only a dollar or two extra. You do of course need a converter for that AC socket.

Cupie · Guru

The Travelling Dillberries wrote:
laurieoz wrote:
Possum3 wrote:
Laurie you will need to check voltage with a voltmeter - Eight year old AGM Batteries would definitely be near the end of their life.
Hi
I have had the batterys disconnected for 4 days
Still 12.83 Volts today
Can the voltage stay up but the capacity of the batterys drop?
Is testing the voltage at rest the only way to test the remaining capacity?
Laurie

-- Edited by laurieoz on Monday 1st of August 2022 06:56:28 PM
To answer your question, testing voltage only gives an indication that the battery may be ok, to be certain they have more life, take them to a battery house and have each one load tested.

I recently took my 5YO 135 kWh Giant AGM battery to Battery World to get a free battery check. (reason .. the voltage on float which has been steady for years suddenly started to vary .. Smart Charger or Battery?)

They kept it for a few days & did two discharge tests. The printed read outs that they provided showed that the battery was down to 50% capacity.

Except for the $135 parking ticket that I got, this was a very economical way to check the battery & Battery World put no pressure on me to buy one of their batteries.

I'll just wait until just before my next outing in October to order another from Aussie Batteries & Solar.

Whenarewethere · Guru

Cupie wrote:
Except for the $135 parking ticket that I got, this was a very economical way to check the battery & Battery World put no pressure on me to buy one of their batteries.

$135 amortised over 4 years is only $33.75

swamp · Senior Member

hi
battery capacity is defined by consumption .
Remember use a defined load light bulbs =5 amps on a fully charged battery . Measure the time it takes to get to 12.oovolts /50% capacity
Should be say 10 hrs to achieve 50a/hr consumption .
So once achieved 12.oo volt calculate amps x time = a/hr capacity available to you .

Aus-Kiwi · Guru

I think less brain power etc ?? Buy some NEW batteries! 8 years is heaps !! Like a Centurion running a marathon . Cliff Young !!

laurieoz · Senior Member

Thanks
I ordered two new batterys on Friday
They were holding charge ok but now hold charge for 3 days and then voltage drops with everything turned off

Battery monitoring system: You enter the capacity of the batterys when fully charged then you can see the state of charge each day
What happens when the batterys are a couple of years old and they are not 200 ahr any more?.
The SOC would not be correct anymore and would be actually less than the SOC on the meter.
What do you do to compensate?

Cupie · Guru

laurieoz wrote:
Thanks
I ordered two new batterys on Friday
They were holding charge ok but now hold charge for 3 days and then voltage drops with everything turned off

Battery monitoring system: You enter the capacity of the batterys when fully charged then you can see the state of charge each day
What happens when the batterys are a couple of years old and they are not 200 ahr any more?.
The SOC would not be correct anymore and would be actually less than the SOC on the meter.
What do you do to compensate?

Good decision.

I too ordered a new battery.

I chose a 140Ah Giant AGM from Aussie Batteries & Solar, delivered for $309.

Whenarewethere · Guru

Annually.

Charge batteries, let them sit for 24 hour to stabilise, put a 20 hour load on the batteries & measure. One battery at a time.

laurieoz · Senior Member

So the SOC reading is pretty much useless??
Better to look at the voltage?
With voltage, it will be lower than actual voltage at rest , so you would be safer
Is this the right assumption ?
Laurie

-- Edited by laurieoz on Monday 8th of August 2022 03:26:42 PM

Aus-Kiwi · Guru

Could try a welder and put 80 amps through . Stand back . May get another few months ?

Jaahn · Guru

laurieoz wrote:
So the SOC reading is pretty much useless??
Better to look at the voltage?
With voltage, it will be lower than actual voltage at rest , so you would be safer
Is this the right assumption ?
Laurie
-- Edited by laurieoz on Monday 8th of August 2022 03:26:42 PM

Hi Laurie smile

It is hard to fathom the relevance of some answers given on here sometimes ??? confuse But here is mine. Some battery SOC meters are not very good.

You can get a quality battery monitor like a Victron BVM 700 series, several models available and current shunt ! They count the current in and out to give an accurate SOC. If they are set up correctly they will correct for the loss of capacity with time by monitoring the amount of charge to get back to full each time. A bit expensive but people like the certainty of a good readout of state of charge. blankstare

https://www.victronenergy.com/battery-monitors

The battery voltage does go up and down for several reasons including how much current is being used at the time and how much solar is being put in. So a reading at any time is dependant on what is happening. However if you have a good voltage readout where you can see it, and you know what is going on at the time, eg loads, or sun or pugged in, you get a 'feel' for your system and can have a good idea of how it is going. I do that, and if something looks out of wack I look into it. My wife has a good idea of it too. aww

Cheers Jaahn

-- Edited by Jaahn on Tuesday 9th of August 2022 09:22:34 AM

Whenarewethere · Guru

Agree.

laurieoz · Senior Member

If they are set up correctly they will correct for the loss of capacity with time by monitoring the amount of charge to get back to full each time.

Hi Jaahn
Thanks for that
Did no realize the above
Laurie

TimTim · Guru

laurieoz wrote:
If they are set up correctly they will correct for the loss of capacity with time by monitoring the amount of charge to get back to full each time.

Hi Jaahn
Thanks for that
Did no realize the above
Laurie

Hi Laurie, if you read back through the posts you will see mention of testing the batteries over 20 hours. Generally, for a new battery to be rated at say 100Ah it must be able to produce 5A for a period of 20 hours. But, if you were to put a 10A load on it then it would not run for 10 hours, a 50A load would not run for 2 hours and a 100A load would not run for 1 hour. The rate of discharge is not linear.

If not using a high current draw then of course the above doesnt matter but a good point that Jaahn pointed out is having a feel for your system and getting an idea of what it is capable of.

In relation to your previous question of With voltage, will it be lower than actual voltage at rest, so you will be safer. Is this the right assumption? If I am correct I think you are are referring to the voltage drop that can be seen at the terminals when a battery is under load. So say you are running appliances through your inverter and for instance you do not want to run your battery below 50% but your multi meter or other devices are showing say 12.06V as per Jaahns table that he posted. Then yes if if your turned off the current draw and let your battery rest the voltage will climb to show that battery is indeed above 50% or safer than going below the 50% mark as you put it. smile

Just for clarification I have merely used 50% as a reference as you can actually run an AGM battery down below 50%.

dave48 · Senior Member

Hi. We have a couple of 140 Ahr batteries in our RV from Aussie batteries and they are about 3 years old and getting down a bit. I thought I'd try one of the battery chargers/desulfators for $60 as it was cheaper than buying new ones. Very very skeptical about the whole thing but let's give it a try. After going through cycles for about 18 hours I'm totally surprised that they have gone from about 60 percent to 100 if I believe all the instruments. Put them in and it's just like having new batteries again. Won't work of course in all cases but I as impressed

Whenarewethere · Guru

& how long did they last on a 20 hour load?

dave48 · Senior Member

I put the 2 in and ran the Engel freezer on -18 all day and night and put the tv on for 5 hours. That's the only test I could do. At the start of the day they were on full ( 13 } volts and leaving everything going the next morning before the MPPT controller started they were on 12.4V. That's the only test I did but it was an enormous improvement on before

TimTim · Guru

Well as long as hey are providing enough power for you with a bit to spare then all well and good. At 12.4v the following morning you are at about 75% so you have plenty of capacity to spare.

With reference to having a charger with a desulphurisation mode, yes they do work but not in all cases as it depends on how the battery has been used. I have one and it has worked great for me even though I have abused two of my testing batteries. Thanks for reminding me as it is one solution that can be used when people are finding that their batteries appear to be losing capacity.

Jaahn · Guru

dave48 wrote:
Hi. We have a couple of 140 Ahr batteries in our RV from Aussie batteries and they are about 3 years old and getting down a bit. I thought I'd try one of the battery chargers/desulfators for $60 as it was cheaper than buying new ones. Very very skeptical about the whole thing but let's give it a try. After going through cycles for about 18 hours I'm totally surprised that they have gone from about 60 percent to 100 if I believe all the instruments. Put them in and it's just like having new batteries again. Won't work of course in all cases but I as impressed

Hi dave smile

I am glad you had success with this. I have not been so lucky.

My comment would be that you should look at your battery charging systems to prevent the batteries getting sulphated in the first place. A good effective battery charger and/or solar charger should prevent sulphating again. IMHO many caravan chargers are rubbish and just DC power supplies for on mains power and do not correctly charge at all. For the cost of a correct multi stage charger you will save your batteries and should get years more life out of them.

My single Aussie Battery 140Ah AGM is older than that and is not noticeably getting down. It charges off the alternator with a VSR and from solar with a MPPT controller. It has a simple power supply too if we stay in a van park but that is not a charger.

What are your chargers now ??

Jaahn

Whenarewethere · Guru

Do you know roughly the minutes on minutes off cycle of the freezer. My guess is roughly 50:50.

If it is a Waeco CFX freezer 40 to 65 litres while the compressor is running it properly using about 4.5 - 5.0 amps.

So let's say 2.5AH per hour. Might help working out you battery resources.

I did extensive tests on my tiny 28L Waeco fridge & it use only a little bit less energy than the larger models.

A bit of testing information on my fridge:

https://thegreynomads.activeboard.com/t65059593/extra-fridge-insulation-wattage-test/

Warren-Pat_01 · Guru

Hi laurieoz,
There's lots of useful info above but I would seriously suggest you don't take Mike Harding's advice of taking the battery down to 10.5v as this will damage any battery.
Taking Yaahn's graph into account will give you an indication as to why. I know some compressor car fridges have cutouts set to 10.5v, but you won't be able to start a car with that voltage.

A headlight globe is a good load - I have one in my gear set so I can run the filaments separately or both together. Just keep it away from anything flammable.

Tony Bev · Guru

I am not a techi, but this is how I tested my AGM batteries, (I was parked up at home, not using the RV)
I am also going from memory, so do not quote me chapter and verse

With the 12 volt compressor fridge on, (and door open), I turned about 6 to 8 lights on, to so that there was 5 amps coming from the batteries.
I isolated the solar so that nothing was going into the batteries.

After 8 hours the batteries were down to about 12.2 volts, indicating that 40 amp hours (8 hours X 5 amp load), was all I was going to get out of 2 X 120 AH batteries.

With a dumb 240 volt charger, and reading the amps going in every hour, (to give an average amps for that hour), I put in approximately 40 amps, before the batteries went into float

Removing the batteries and checking them 48 hours later, one battery showed 12.8 volts, but the other one only showed around 12 volt

That told me that one battery was no longer suitable

Hope that this info is useful to someone