Hi All Well we finally got away in our new (2011 Goldstream RV) and had a bit of trouble sorting out solar, charge, etc. Finally worked out that we cannot leave the Anderson plug or the 7 pin plug attached to the vehicle for the solar to charge the van battery. Anyway the battery (new AGM 120ah) went down to 12.1 before we sorted it. Wondering how low can a battery get without causing permanent damage. by the way we stayed at Carmila Beach for 4 days. Great place except the dump point was really full. A major health hazard. I will email them tomorrow to let them know.
Cheers Kim
Old Col said
09:43 PM Jun 21, 2015
12.1v is about 55% for long life that's about as low as you should go
DeBe said
11:55 AM Jun 22, 2015
The main point is if you do happen to flatten a battery, is don't leave it flat. Charge it up as soon as possible & it will be ok. If they are left too long then they wont recover properly.
mickm said
05:44 PM Jun 22, 2015
State of Charge
Sealed or Flooded Lead Acid
Gel battery
AGM battery
100%
12.70+
12.85+
12.80+
75%
12.40
12.65
12.60
50%
12.20
12.35
12.30
25%
12.00
12.00
12.00
0%
11.80
Every time you run below 50% you are seriously reducing the life of the battery.
Peter_n_Margaret said
01:25 AM Jun 23, 2015
"Every time you run below 50% you are seriously reducing the life of the battery."
I don't believe that is true at all.
Capacity testing on AGMs takes them down to 10.5V. That is considered 0% SOC. That can be repeated many times without damage.
The important point, as DeBe says is to recharge them fully as soon as possible.
Cheers,
Peter
Izabarack said
06:51 AM Jun 23, 2015
mickm wrote:Every time you run below 50% you are seriously reducing the life of the battery.
It's not like a line in the sand. The deeper the discharge, the fewer the number of charge/recharge cycles the battery is likely to tolerate. Many a battery tech sheet says a deep cycle battery discharged to 20% state of charge will only last 500 cycles. At that rate, down to 20% once a week, the battery will only last 10 years.
I had a low tech Flooded deep cycle down to under 11.5 Volts quite regularly (Engel fridges run all the way down to about 11 volts) and that battery lasted 6 years.
Best advice given so far is to recharge as soon as possible.
Iza
-- Edited by Izabarack on Tuesday 23rd of June 2015 06:52:17 AM
gandk said
07:33 AM Jun 23, 2015
Thank you to all, as I really didn't know how it all worked. Actually still had trouble so shall post a newbie on the solar site.
Peter_n_Margaret said
01:01 AM Jun 24, 2015
The other thing to be aware of is that discharging to 20% provides DOUBLE the power to discharging to 60%, so you only need half as many batteries and only need half the number of cycles to break even.
Work life out in kWhs of power delivered, not number of cycles for a real comparison.
Cheers,
Peter
gandk said
06:57 AM Jun 24, 2015
Thanks Peter! I think. I shall have to work on that suggestion as I said I am definitely not the brightest star in the sky.
Ta
Kim
Ondabeach said
08:35 AM Jun 24, 2015
Actually Peter, the thing is that continually discharging your battery to 20% will GREATLY reduce the life of your battery... by 90% in fact!!!
Just google 'AGM battery discharge depth vs cycles' and you'll see the same thing everywhere.
The lower you discharge your batteries, the shorter their life.
The longer you leave them even partially discharged, the shorter their life.
To maximise your battery life, keep them as close to fully charged as possible.
Our van will be parked at home for a few months,. We only have one battery, so I have just disconnected one of the terminals. Normally the roof top solar panels would keep the battery charged, but I have covered the van so no solar.
Have I done the right thing???
Jay&Dee
Ondabeach said
12:11 PM Jun 24, 2015
Yes JayDee, in that situation it's best to disconnect it as you have done. Just put them on charge overnight to make sure they're fully charged.
If they're AGM or other type of deep cycle batt then they'll be fine for a few months.
If they're the old style of non-sealed lead acid batts with the caps for topping up water, then it'd be wise to put them on charge overnight once a month.
Izabarack said
01:38 PM Jun 24, 2015
Ondabeach wrote:
The lower you discharge your batteries, the shorter their life.
.
Not sure how you might measure "life" in that statement. Batteries are good for storing so much power and delivering that power back, before their ability to store and deliver starts to fall off. Discharging to 60% and charging back to full can be considered a cycle. Discharging to 20% before recharge can be considered a cycle. When looking at amount of energy stored and delivered, two cycles of 60% are equivalent to one cycle of 20%. Every charge and recharge incident degrades the battery by some small amount. The little amounts accumulate over time in a somewhat linear fashion. That is why very small discharge cycles can be done lots of times and large discharge cycles can be done fewer times. As Peter says "Work life out in kWhs of power delivered, not number of cycles for a real comparison".
Iza
Ondabeach said
02:52 PM Jun 24, 2015
Whether you discharge to 20% or 60% before recharging, it is still a cycle. A cycle is defined as a period of discharge followed by a period of charge, ideally to full capacity.
While a battery is discharging, the sulphuric acid, which is the electrolyte, chemically reacts with the lead plates to create lead sulphate, which builds up on the surface of the plates.
When the battery is recharged, most of the lead sulphate is converted back into sulphuric acid and lead, but some of it will crystalize and will not reconvert.
The deeper you discharge a battery, the thicker the layer of lead sulphate build up, and the less of the lead sulphate that will convert back into sulphuric acid when the battery is recharged.
The longer a battery remains in a state of even partial discharge, the more of the lead sulphate on the plate surfaces will crystalize, which is why a battery left discharged for a long time will no longer accept a charge, because too much of the lead sulphate will have crystalized and no longer be able to be reconverted to electrolyte and acid.
So the bottom line is that the more deeply you discharge your battery, the fewer discharge charge cycles it will endure, in other words, the shorter it's life.
Happywanderer said
03:10 PM Jun 24, 2015
Some good info here. Time for a Battery Sub forum I reckon.
Izabarack said
04:03 PM Jun 24, 2015
Ondabeach wrote:
Whether you discharge to 20% or 60% before recharging, it is still a cycle. A cycle is defined as a period of discharge followed by a period of charge, ideally to full capacity.
So the bottom line is that the more deeply you discharge your battery, the fewer discharge charge cycles it will endure, in other words, the shorter it's life.
All cycles are not equal, Steve. A cycle to 20% is not equal to a cycle to 60%. To talk cycles and try to define life in cycle terms is mostly meaningless. Yes, during each recharge event, a little less lead sulphate is converted, as I explained above. The rate at which the degradation occurs is pretty well linear to the amount of conversion that occurs during a single event where the battery is discharged from some charge level. A little use, a little degradation; a lot of draw and a lot more degradation. So the number of "cycles" is just a count of the number of charges the battery receives after a discharge of some value; nothing to do with some prediction of "life".
Crystalisation of lead sulphate is a slow process and can largely be avoided by not leaving a battery in a discharged state any longer than possible. Crystalised lead sulphate effectively forms a crust on the plates and does not allow the electrolyte to contact the active surface of the plates. Hence the useful advice that a battery should be recharged as soon as possible after any level of discharge, and given a regular tickle up when in storage situation.
Iza
-- Edited by Izabarack on Wednesday 24th of June 2015 04:05:46 PM
Ondabeach said
04:43 PM Jun 24, 2015
Yes Iza, 20% is different to 60%, and no, you can't define a battery's life in a precise number of cycles. There is no definitive way to predict the life of a battery, but the manufacturers use 'cycles' as a yard stick because it's the most definitive and succinct method they have.
The crucial facts remain that the deeper you discharge a battery, and the longer it is not in a fully charged state, the shorter it's life will be. Any time that a battery is not fully charged then there will be some lead sulphate present, and some of it will be crystalizing.
So, more time a battery spends near fully charged the longer it will last.
Peter_n_Margaret said
06:31 PM Jun 25, 2015
Ondabeach wrote:
So the bottom line is that the more deeply you discharge your battery, the fewer discharge charge cycles it will endure, in other words, the shorter it's life.
This is exactly the same as saying if you drive to the next city instead of just driving to the shops you will get less TRIPS from a tank of petrol.
A battery works in much the same way.
The graph you posted has the information to calculate the differences. Measuring the life in Ahs or Whs will indicate the power the battery delivers in its life - like a car, we are interested in fuel range, not how many trips we have.
Shallower discharges give slightly better life it is true, but that may require buying and carrying several batteries instead of just one.
To get back to the OP, discharging your battery to a low state will not DAMAGE it, it will simply use more of the total fuel that it can deliver over its lifetime.
And do recharge it fully as soon as possible. Leaving it flat will damage it.
Cheers,
Peter
-- Edited by Peter_n_Margaret on Thursday 25th of June 2015 06:32:35 PM
-- Edited by Peter_n_Margaret on Thursday 25th of June 2015 06:42:59 PM
Ondabeach said
08:11 PM Jun 25, 2015
ROFL... Oops, I just wet myself laughing
Izabarack said
10:51 AM Jun 26, 2015
Ondabeach wrote:
........the manufacturers use 'cycles' as a yard stick because it's the most definitive and succinct method they have.
Any time that a battery is not fully charged then there will be some lead sulphate present, and some of it will be crystalizing.
So, more time a battery spends near fully charged the longer it will last.
Manufactures use graphs of cycles as page fillers in their ads. Cycles as per your definition are categorical but graphs of cycles add a dimensional component to the advertising. Interpretation of the graphs as an indication of how much power a battery can store and subsequently deliver allow a pretty good definition of the design capacity of a battery. "Life" is a pretty meaningless attribute to apply to a battery as it suggests some time component. In my example earlier, 500 deep discharge cycles out of a battery may take 10 years to complete yet most batteries degrade to the point of throwaway as a function of plain old age, well before 10 years. Uninterrupted Power Supply batteries, even newer technology ones, are replaced after a relatively short period despite being held at and charged to a full state all their "life". Are you suggesting that batteries that are always full charged, that is, never cycled, will last forever?
Iza
Ondabeach said
11:31 AM Jun 26, 2015
Izabarack wrote:
Manufactures use graphs of cycles as page fillers in their ads.
Iza
Now that's just a really silly thing to say Iza
Peter, you seem to be under the impression that a battery will deliver close to the same number of KW hours in it's lifetime regardless of how deeply you discharge it. That is simply not true, to use a fuel economy analogy, you're suggesting that you can get the same mileage from a tank of gas regardless of speed, load and terrain.
Izabarack said
02:08 PM Jun 26, 2015
Ondabeach wrote:
....., to use a fuel economy analogy, ...............
That's an analogy that does not work, Steve. Fuel usage varies in accordance with several factors other than how much you use before filling the tank again. A water analogy might work if you could explain how water disappears if you empty more each time before you refill.
Iza
Peter_n_Margaret said
06:00 PM Jun 26, 2015
This is becoming tedious.
To use your graph Steve......and using a 100Ah battery as an example.... If you discharge that battery by 80Ah between charges EVERY time you use it, your graph shows it will deliver about 500 cycles @ 80Ah each = about 4,000Ah over its lifetime. If you choose to discharge it by only 20Ah between charges EVERY time you use it, your graph shows it will deliver about 2,800 cycles @ 20Ah each = about 5,600Ah over its lifetime.
"Actually Peter, the thing is that continually discharging your battery to 20% will GREATLY reduce the life of your battery... by 90% in fact!!!"
No, not a 90% reduction in capacity, closer to 28% actually, for this quite extreme example.
Then, if you wish to take advantage of that extra life and you need the 80Ah between charges, you will need to carry 4 of those 100Ah batteries instead of one.
That is about 120kg instead of 30kg to lug about and about $1,200 instead of $300 to spend each time they need replacing.
We can each decide which of those options appeals to us best.
Cheers,
Peter
gandk said
07:28 AM Jun 27, 2015
I have never had such a reaction from so many men before. Must tell my husband.
Cheers
Kim
Ondabeach said
07:53 AM Jun 27, 2015
Peter_n_Margaret wrote:
This is becoming tedious.
But... you just couldn't resist misquoting again hey Pete?
No one has suggested only discharging batts by 20%, I recommend not going below 50%.
Santa said
08:54 AM Jun 27, 2015
These battery threads really are a popcorn lovers dream, there is certainly no shortage of them, they go on interminably, everyone is an expert, and, at the end of the discussion everyone is either confused or angry, perhaps a little of both.
Love it.
Peter_n_Margaret said
11:46 PM Jun 27, 2015
Ondabeach wrote:
But... you just couldn't resist misquoting again hey Pete?
No one has suggested only discharging batts by 20%, I recommend not going below 50%.
The only time I quoted you Steve was when you said......
"Actually Peter, the thing is that continually discharging your battery to 20% will GREATLY reduce the life of your battery... by 90% in fact!!!"
This is a common statement about deep cycle batteries and AGMs in particular, but it is an urban myth, it is misleading, it is not correct, it is just wrong and there is no data to support it by manufacturers or any one else, but quote it often enough and some people will start to believe it.
Look like all the world's battery manufacturers are pretty clueless Pete, you could save them a fortune in all that silly testing they do.
Amp Hour lifetime delivery comparison for a 100 amp hour AGM battery based on data from battery manufacturers.
***********************************
Discharge down to 20%
500 cycles @ 80 Amp Hours = 40,000 Amp Hours
***********************************
Discharge down to 50%
1100 cycles @ 50 Amp Hours = 55,000 Amp Hours
***********************************
40 x 1.375 = 55
So only discharging your batteries down to 50% will give 37.5% more usable power during the lifetime of a battery compared to discharging down to 20%.
Not my opinion, just cold hard scientific fact, proven not by me, but by the companies that make the batteries.
Ontos45 said
12:51 PM Jun 28, 2015
Below is a link to wheelchair Gel and Glass fast battery charging that may interest some. Wheelchair batteries get hammered specially indoor/outdoor versions.
Hi All Well we finally got away in our new (2011 Goldstream RV) and had a bit of trouble sorting out solar, charge, etc. Finally worked out that we cannot leave the Anderson plug or the 7 pin plug attached to the vehicle for the solar to charge the van battery. Anyway the battery (new AGM 120ah) went down to 12.1 before we sorted it. Wondering how low can a battery get without causing permanent damage. by the way we stayed at Carmila Beach for 4 days. Great place except the dump point was really full. A major health hazard. I will email them tomorrow to let them know.
Cheers Kim
12.1v is about 55% for long life that's about as low as you should go
Every time you run below 50% you are seriously reducing the life of the battery.
"Every time you run below 50% you are seriously reducing the life of the battery."
I don't believe that is true at all.
Capacity testing on AGMs takes them down to 10.5V. That is considered 0% SOC. That can be repeated many times without damage.
The important point, as DeBe says is to recharge them fully as soon as possible.
Cheers,
Peter
It's not like a line in the sand. The deeper the discharge, the fewer the number of charge/recharge cycles the battery is likely to tolerate. Many a battery tech sheet says a deep cycle battery discharged to 20% state of charge will only last 500 cycles. At that rate, down to 20% once a week, the battery will only last 10 years.
I had a low tech Flooded deep cycle down to under 11.5 Volts quite regularly (Engel fridges run all the way down to about 11 volts) and that battery lasted 6 years.
Best advice given so far is to recharge as soon as possible.
Iza
-- Edited by Izabarack on Tuesday 23rd of June 2015 06:52:17 AM
Work life out in kWhs of power delivered, not number of cycles for a real comparison.
Cheers,
Peter
Thanks Peter! I think. I shall have to work on that suggestion as I said I am definitely not the brightest star in the sky.
Ta
Kim
Actually Peter, the thing is that continually discharging your battery to 20% will GREATLY reduce the life of your battery... by 90% in fact!!!
Just google 'AGM battery discharge depth vs cycles' and you'll see the same thing everywhere.
The lower you discharge your batteries, the shorter their life.
The longer you leave them even partially discharged, the shorter their life.
To maximise your battery life, keep them as close to fully charged as possible.
Have I done the right thing???
Jay&Dee
Yes JayDee, in that situation it's best to disconnect it as you have done. Just put them on charge overnight to make sure they're fully charged.
If they're AGM or other type of deep cycle batt then they'll be fine for a few months.
If they're the old style of non-sealed lead acid batts with the caps for topping up water, then it'd be wise to put them on charge overnight once a month.
Not sure how you might measure "life" in that statement. Batteries are good for storing so much power and delivering that power back, before their ability to store and deliver starts to fall off. Discharging to 60% and charging back to full can be considered a cycle. Discharging to 20% before recharge can be considered a cycle. When looking at amount of energy stored and delivered, two cycles of 60% are equivalent to one cycle of 20%. Every charge and recharge incident degrades the battery by some small amount. The little amounts accumulate over time in a somewhat linear fashion. That is why very small discharge cycles can be done lots of times and large discharge cycles can be done fewer times. As Peter says "Work life out in kWhs of power delivered, not number of cycles for a real comparison".
Iza
Whether you discharge to 20% or 60% before recharging, it is still a cycle. A cycle is defined as a period of discharge followed by a period of charge, ideally to full capacity.
While a battery is discharging, the sulphuric acid, which is the electrolyte, chemically reacts with the lead plates to create lead sulphate, which builds up on the surface of the plates.
When the battery is recharged, most of the lead sulphate is converted back into sulphuric acid and lead, but some of it will crystalize and will not reconvert.
The deeper you discharge a battery, the thicker the layer of lead sulphate build up, and the less of the lead sulphate that will convert back into sulphuric acid when the battery is recharged.
The longer a battery remains in a state of even partial discharge, the more of the lead sulphate on the plate surfaces will crystalize, which is why a battery left discharged for a long time will no longer accept a charge, because too much of the lead sulphate will have crystalized and no longer be able to be reconverted to electrolyte and acid.
So the bottom line is that the more deeply you discharge your battery, the fewer discharge charge cycles it will endure, in other words, the shorter it's life.
All cycles are not equal, Steve. A cycle to 20% is not equal to a cycle to 60%. To talk cycles and try to define life in cycle terms is mostly meaningless. Yes, during each recharge event, a little less lead sulphate is converted, as I explained above. The rate at which the degradation occurs is pretty well linear to the amount of conversion that occurs during a single event where the battery is discharged from some charge level. A little use, a little degradation; a lot of draw and a lot more degradation. So the number of "cycles" is just a count of the number of charges the battery receives after a discharge of some value; nothing to do with some prediction of "life".
Crystalisation of lead sulphate is a slow process and can largely be avoided by not leaving a battery in a discharged state any longer than possible. Crystalised lead sulphate effectively forms a crust on the plates and does not allow the electrolyte to contact the active surface of the plates. Hence the useful advice that a battery should be recharged as soon as possible after any level of discharge, and given a regular tickle up when in storage situation.
Iza
-- Edited by Izabarack on Wednesday 24th of June 2015 04:05:46 PM
Yes Iza, 20% is different to 60%, and no, you can't define a battery's life in a precise number of cycles. There is no definitive way to predict the life of a battery, but the manufacturers use 'cycles' as a yard stick because it's the most definitive and succinct method they have.
The crucial facts remain that the deeper you discharge a battery, and the longer it is not in a fully charged state, the shorter it's life will be. Any time that a battery is not fully charged then there will be some lead sulphate present, and some of it will be crystalizing.
So, more time a battery spends near fully charged the longer it will last.
This is exactly the same as saying if you drive to the next city instead of just driving to the shops you will get less TRIPS from a tank of petrol.
A battery works in much the same way.
The graph you posted has the information to calculate the differences. Measuring the life in Ahs or Whs will indicate the power the battery delivers in its life - like a car, we are interested in fuel range, not how many trips we have.
Shallower discharges give slightly better life it is true, but that may require buying and carrying several batteries instead of just one.
To get back to the OP, discharging your battery to a low state will not DAMAGE it, it will simply use more of the total fuel that it can deliver over its lifetime.
And do recharge it fully as soon as possible. Leaving it flat will damage it.
Cheers,
Peter
-- Edited by Peter_n_Margaret on Thursday 25th of June 2015 06:32:35 PM
-- Edited by Peter_n_Margaret on Thursday 25th of June 2015 06:42:59 PM
ROFL... Oops, I just wet myself laughing
Manufactures use graphs of cycles as page fillers in their ads. Cycles as per your definition are categorical but graphs of cycles add a dimensional component to the advertising. Interpretation of the graphs as an indication of how much power a battery can store and subsequently deliver allow a pretty good definition of the design capacity of a battery. "Life" is a pretty meaningless attribute to apply to a battery as it suggests some time component. In my example earlier, 500 deep discharge cycles out of a battery may take 10 years to complete yet most batteries degrade to the point of throwaway as a function of plain old age, well before 10 years. Uninterrupted Power Supply batteries, even newer technology ones, are replaced after a relatively short period despite being held at and charged to a full state all their "life". Are you suggesting that batteries that are always full charged, that is, never cycled, will last forever?
Iza
Now that's just a really silly thing to say Iza
Peter, you seem to be under the impression that a battery will deliver close to the same number of KW hours in it's lifetime regardless of how deeply you discharge it. That is simply not true, to use a fuel economy analogy, you're suggesting that you can get the same mileage from a tank of gas regardless of speed, load and terrain.
That's an analogy that does not work, Steve. Fuel usage varies in accordance with several factors other than how much you use before filling the tank again. A water analogy might work if you could explain how water disappears if you empty more each time before you refill.
Iza
This is becoming tedious.
To use your graph Steve......and using a 100Ah battery as an example....
If you discharge that battery by 80Ah between charges EVERY time you use it, your graph shows it will deliver about 500 cycles @ 80Ah each = about 4,000Ah over its lifetime.
If you choose to discharge it by only 20Ah between charges EVERY time you use it, your graph shows it will deliver about 2,800 cycles @ 20Ah each = about 5,600Ah over its lifetime.
"Actually Peter, the thing is that continually discharging your battery to 20% will GREATLY reduce the life of your battery... by 90% in fact!!!"
No, not a 90% reduction in capacity, closer to 28% actually, for this quite extreme example.
Then, if you wish to take advantage of that extra life and you need the 80Ah between charges, you will need to carry 4 of those 100Ah batteries instead of one.
That is about 120kg instead of 30kg to lug about and about $1,200 instead of $300 to spend each time they need replacing.
We can each decide which of those options appeals to us best.
Cheers,
Peter
Cheers
Kim
But... you just couldn't resist misquoting again hey Pete?
No one has suggested only discharging batts by 20%, I recommend not going below 50%.
These battery threads really are a popcorn lovers dream, there is certainly no shortage of them, they go on interminably, everyone is an expert, and, at the end of the discussion everyone is either confused or angry, perhaps a little of both.
Love it.
The only time I quoted you Steve was when you said......
"Actually Peter, the thing is that continually discharging your battery to 20% will GREATLY reduce the life of your battery... by 90% in fact!!!"
This is a common statement about deep cycle batteries and AGMs in particular, but it is an urban myth, it is misleading, it is not correct, it is just wrong and there is no data to support it by manufacturers or any one else, but quote it often enough and some people will start to believe it.
Cheers,
Peter
Just a few urban myths for ya Pete
https://www.google.com.au/search?q=agm+battery+cycle+discharge+curve&biw=1280&bih=623&tbm=isch&tbo=u&source=univ&sa=X&ei=5CiPVZSdIoTl8gXM6YPgBw&sqi=2&ved=0CCMQsAQ#imgrc=_
Look like all the world's battery manufacturers are pretty clueless Pete, you could save them a fortune in all that silly testing they do.
Amp Hour lifetime delivery comparison for a 100 amp hour AGM battery based on data from battery manufacturers.
***********************************
Discharge down to 20%
500 cycles @ 80 Amp Hours = 40,000 Amp Hours
***********************************
Discharge down to 50%
1100 cycles @ 50 Amp Hours = 55,000 Amp Hours
***********************************
40 x 1.375 = 55
So only discharging your batteries down to 50% will give 37.5% more usable power during the lifetime of a battery compared to discharging down to 20%.
Not my opinion, just cold hard scientific fact, proven not by me, but by the companies that make the batteries.
Below is a link to wheelchair Gel and Glass fast battery charging that may interest some. Wheelchair batteries get hammered specially indoor/outdoor versions.
http://www.wheelchairdriver.com/fast-charge-your-power-wheelchair.htm