Lithium upgrade

The van has a BMPRO-35HA controller and a trek monitor, so I do have a means of keeping an eye without grovelling around under the seat with a multimeter. Not quite as convenient or informative as the Bluetooth but I’ll look into the victron monitor.

Cheers
Steve

The BMV 712 Smart has bluetooth built in, and uses a virtually immeasurable amount of power to run. I have one with my 120Ah portable lithium pack, and go a couple of months with almost no discharge. It's fully configurable and provides a huge amount of info from the phone app.
I'd save my money and do something similar, that way if you change your batteries down the track, you'll still have the monitor.

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He's not actually downsizing. With recommended depth-of-discharge values of 80% for Lithium and 50% for AGM, he will realise 160Ah from his Lithium compared to only 150Ah from the AGM. Plus the Lithium maintains its voltage level to discharge much better than AGM's.

There's no valid reason why AGM batteries need to be restricted to half of their nameplate capacity. There's no penalty for deeper discharge. It's actually a significant downsize.

A bad aspect of taking an AGM down to 50% is that it is near to about 12.2 volts...now a lithium at 80% is still at 13 volts. Vast majority of dc equipment run far better and more efficient with voltages in the high 12,s...particularly fridges.

Bigfish, I'm not really making a comparison. The benefits of LiFePO4 are well understood. I just don't see any benefit in restricting a capable battery to half of it's nameplate. The majority of appliances are happy enough just below 12V. This is only the nominal voltage. It isn't a sound enough reason to only use half of a battery.

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Croc,
There is a penalty for deeper discharge for any battery type. Even if you "cannot see it" the effect of deeper discharge is well established as reduction in usable battery life. It is a complex relationship dependant on such things as charge/discharge rates, number of partial cycles, temperature and individual manufacture practices. So there are no fixed formulas but there is general industry agreement that optimum DOD figure are 50% for lead-acid (including AGM) and 80% for lithium.
Of course these values can be exceeded but at the cost of battery usable life. Even so, it may be attractive for some users to "get more out of their battery" by deeper discharge and therefore gain more delivered Ampere-hours and carry smaller rated batteries by being prepared to replace batteries more often. But the recommendations of DOD are made for the average user's expectations.

I understand how batteries work Allan. All other parameters being equal then the penalty for deeper discharge is a reduction in life cycles not life span. This doesn't matter because shallow discharges require a larger number of cycles for the same energy delivery. 1000 cycles at 40% delivers the same energy output as as 500 cycles at 80%. It's a zero sum game.


AGM Cycle Live vs DoD

A chart for a typical AGM battery from a reputable supplier shows that for a 100Ah battery the total no of Ah delivered of its life at 50% is 1300 x 0.5 x100 = 65,000Ah.

The same battery at 90% is 700 x 0.9 x 100 = 63,000Ah.

There is hardly any difference.

There are items that don't perform as they should when the voltage drops so having a higher constant voltage is better than a decreasing one. Also I though when I was researching agm's some yrs ago that yes you get the same ah delivered for its lifespan wether you run it down to 50% or say 30% for eg but you also risk damaging the battery which can shorten it's overall lifespan by regularly running it down to its lower limit so best to stay around 50%. In saying that it's just a risk not a guarantee that it will be damaged so I always ran mine no lower than 50%. The quality of the battery would have a lot to do with its vulnerability as well I expect.

Batt...my 85 litre fridge is an example of a piece of equipment that likes higher voltages. It behaves perfectly fine on anything over 12.5. Under this the compressor runs longer. Fridges would be by far the biggest power user of any 12 volt system..apart from the glampers who use a hair dryer or coffee machine . My second last set of fullriver batteries lasted 8 years and still were good. Last set I had for 5 years before swapping to lithium and were at around 90% of original capacity when I sold them. I put this down to the fact that I never took them below 50% and regularly charged them via solar or 240 volt 7 stage charger. If you only go camping a couple of times a year then I reckon you could get away with taking your agms down to 12 volt...if your fridge doesnt mind. Quickly recharge them when getting home and they should be fine. However lithium is very affordable now and just a lot better power source. Great weight saving as well.

There a whole bunch of myths circulating on forums and people just seem to believe them an keep spreading the untruths.

What "damage" is done to a battery?

Damage is something physical like plate material gradually falling off the grids that happens in time , it is a number of factors such as temperature and vibration and electrolyte composition that does this, as well as the ion migration to a lesser point.
Start batteries actually have troughs below the plates to store this sediment so the cell continues to operate until it is high enough to actually short the plates with physical contact of the plates. Vibration can also fatigue the spot welds which leads to sudden death, these are what "dropped a cell" a term thrown in by the google experts actually means.

Sulphation is another killer but this is a physical buld up of a sulphate or a type of salt crystal that is forming continiously on the plates of a lead acid battery and insulates them but it tends to be pushed off by current flow so only reaches crytical thickneses with prolonged periods on standing. To my understanding DOD does not accelerate sulphation but probably the exact opposite if recharged soon after.

You can actually see these crystals inside dead batteries clinging to lead surfaces.

So here is my question,
What physical damage is done to a lead acid battery by deep discharge other than normal ware and tear that is within design parameters?

My understanding of this subject was gathered by several long discussions with a neighbour who was a retired chemical engineer who spent time in R&D for battery companies and petrochemicals.

From the internet...

Why Is Discharging a Car Battery Too Far So Bad?

Even though 80 percent of the capacity remains when a car battery dips to around 10.5 volts, the battery is considered to be fully discharged because taking the cycle any deeper will cause irreversible damage to the plates through excessive sulfation.

While normal sulfation is reversible, excessively draining a battery, or leaving it in a state of discharge, will allow the soft lead sulfate to crystallize. At that point, charging the battery will still cause some of the sulfation to reverse, but any crystallized lead sulfate will remain on the plates. This sulfate cannot, under normal circumstances, return to a solution in the electrolyte, which permanently reduces the available output of the battery.

The other detrimental effect of allowing crystallized lead sulfate to form is that it effectively shortens the lifespan of the battery in an empirically measurable way. If too much of this crystallization is allowed to occur, the battery will no longer be able to provide enough amperage to start the engine, and it will have to be replaced.

Depends on what you read, where you read it and the context, from Batter University for example:

"Permanent sulfation sets in when the battery has been in a low state-of-charge for weeks or months. At this stage, no form of restoration seems possible; however, the recovery yield is not fully understood. To everyone’s amazement, new lead acid batteries can often be fully restored after dwelling in a low-voltage condition for many weeks. Other factors may play a role."

Even batteries being continually cycle in the mid capacity range can sulfate if they are never fully charged.

Like I said, people that dont know read what people that dont know write on the net.
My money is on what an engineer who spent a great deal of their career developing batteries for major companies back in the day when battery cells were allowed to be manufactured in Australia.

Strange statement qldcamper...you say people who dont know about a subject just read about it on the internet and is written by people who dont know! Now people who do know are expected to listen to you because a mate told you!...There are a hell of a lot smarter people on the internet than your mate. I gave you answer to your question that was provided by an electrical engineer.

Sorry Bigfish but Qldcamper has some credence. What electrical engineer claims that 80% of the batteries capacity is below 10.5V. Dug his degree out of a Corn Flakes packet. Sulphation is not caused by discharge. It is the result of depriving the battery of charge.

Croc..I,m also a bit puzzled by that figure...maybe they are talking about some other aspect of its capacity...no idea......

This is from the Yuasa battery site regarding physical damage...

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I'm totally lost! Where did Croc's "80%" and "10.5v" come from. I must have blinked.

Hi AllanB, Bigfish's post ID 914486 a few posts up the page:

"Even though 80 percent of the capacity remains when a car battery dips to around 10.5 volts"

I blinked too but just caught it.

I usually get my so called myths about batteries from the companies that sell the products. So maybe most of them are wrong and supplying false info because most of them say you can shorten the life of their battery if you quite often run it low or don't recharge it for a while in that condition. Anyway I'll stick with the mythical info supplied by the majority of these companies but according to the odd person they have got it all wrong but they're still willing to write it down in black and white on their website go figure what fools.

Batts, how many of these companies dictate this 50% myth. The majority have no such nonsense. The minority, isn't hard to work out. They get to sell twice as many batteries to unsuspecting punters and the argue about warranties.

I have sat on the side of this discussion as I have seen the same thing so many times and yet it still comes up with people quoting different experts. It has also been stated that this engineer etc who designed batteries for X amount of years stated this etc. Personally one would hope the battery manufacturer knows his product so if we look at Full River who many believe is one of the better AGM's on the market what do they indicate?

The below link is to one of their 100Ah AGM life cycles versus depth of discharge graph, ie how long the battery will last at different depths of discharge:

DLife cyclesOD gr

Looking at the graph if you discharge to 50% DOD you get approx 1600 cycles, at 100% DOD you get approx 600 cycles. No instant distruction or sulphation you still get 600 cycles at 100 DOD.

If we look at the 50% DOD, you can put 50Ah in and take 50Ah out 1600 times which equates to 80000Ah in and out of the battery. At 100% we get 60000AH yes a reduction in through put but no instant destruction.

If we look at 80% DOD we get approximately a 1000 cycles or 80000Ah the same as at a 50% DOD, why good question, my theory is their working with a cycle being one discharge cycle per day, therefore we have 1600 days at 50% versus 1000 days at 80% battery age probably then becomes involved ie battery one battery wearing out more due to age whereas the other more due to work.

Bottom line is at 80% the through put is the same, yes the one discharged to 80% DOD is only going to last 1000 days given a daily cycle compared to the 1600 days of the 50% DOD unit, but to discharge to only 50% you need two, discharging to 80% you'll still need two over the same period of time but you only have to carry one at a time.

You can lead a horse to water Bigfish.

And you will never fix stupid either qldcamper.

Yep, stupid people just keep searching the net till they find in writing what they want to hear then defend its credability blindly.

Wise people listen to those with real experience rather than google experts.

I am still learning so am very selective where I actually learn from as I have not yet reached Bigfish's academic level of knowing everything and feeling secure that there is nothing left to learn.

Not really interested in learning about lead acid batteries. 20 years working on very remote solar installs for communication towers taught me all I needed to know. Install, maintenance and fault finding was all in a days work. Retired a couple of years ago and now I only have lithium.. I,ve seen more stuffed agm batteries than you have had hot meals. Glad to hear your still learning...Getting off track now so I,ll catch you later.

Yes your right, wise people listen to those with real experience which is why I refer to the manufacturers technical documentation the same as any good engineer would do. Until you can provided similar documented proof to what the manufacturer has provide showing what he has stated is not correct then I'll disregard what you write as being purely your own personal beliefs and opinions with no actual real data to back it up. If you have the real data to back it up you wouldn't need to revert to bullying and calling people names to try and force feed the rubbish your putting across.

I spent a lot longer than 20 years working with Telcos providing high level technical support to the Technology groups and field staff and know most of the those people have very little real knowledge about anything they work on.

Talking of Telco batteries, I assume Exide is still supplying Telcos here with batteries, the below link is to one of the Telco ranges, interesting the life cycle performance of their battery to 80% discharge is even better than Full Rivers so they must also not know what their talking about.

And yes your right you can lead a horse to water but can't make him drink it, especially when the water your trying to make him drink is bad.

Very true leigh.
I agree about varifying a products specs with the manufacturers literature but I also believe that knowledge gathered in conversations with the very people that developed the manufacturers specs and recomendations has some standing also.

But as we are all aware, if its not on google it cant possibly be correct.

It is a little baffling that after being presented with real data direct from a reputable manufacturer, having the terms explained and then producing the maths behind all this that some can still believe in fairies and deny everything.

Believing this 50% nonsense is the same thing as buying two vehicles and driving them on alternate days. They'll at least last twice as long.

Croc099 I can't supply a number of how many make these claims that's an unreasonable request. You have internet access do some research. I'm no expert on the subject but when some companies are writing this on their sites there must be some truth to it or they're doing themselves out of business for no reason. There is no myth in it just clear cut in the writing.

Thanks Allan. Good to know about the Bluetooth power use.

Becoming a bit clearer now.

3x 100 ah = 240 usable

1x 200 ah 180 usable with tech and $500 less than the above

For another $500 I can get 2x 125 ah batteries, which is 20 ah (200 usable) more than the single 200ah

Looks like the 1x 200 ah battery is the answer

Aaaagh… knew I’d slip up with the maths somewhere ;) yep, I only took 10% off

but… I realise 200 ah lithium is better than 300 agm. I am trying to decide which lithium option

Just clarifying: I currently have 300 ah of agm. 300ah of (3x separate 100 ah lithium) lithium is just one of the lithium options I’m trying to decide on.

I assume with that much battery and solar you have an inverter, if so one consideration would be each battery if they have an internal BMS's should be able to handle the load of the inverter. This may limit your options.

I,ve got 3 x 120a/h ITech lithiums. Have tested all of them and I get a usable 105-107 a/h from each. So a loss of only 13-15%.

I've had 2 x 120ah Itechworld lithiums for a few years now. No complaints, simply do their job.

B.I.L has Renogy lithiums and reports the same (after 1 year).

Mind you, the two 100ah AGMs mine replaced are now 9 and 10 years old, respectively. One is still running well in brother's vehicle, the other runs my pond pump, charged via a solar panel!

Cheers,

Mark

Cheers Bob.

Interesting. I’ll go through the comparative specs.

I fitted a 170ah Renogy in March last yr it's been good so far running a fridge and sometimes a travel buddy oven while parked up. I sometimes use the 240v inverter I wired in to it to recharge 18v makita batteries at home. No bluetooth but I don't need it I think the 100ah has it.

Since when was a LA battery at 10V at 50% DOD or 6V at 80% DOD?
By definition, 100% DOD is 10.5V.
Sorry, but that is a load of crap.
Cheers,
Peter
OKA196 motothome

It appears to be plucked from the internet by a battery expert who doesn't pluck rubbish figures from the internet and apparently can't explain why he posted such rubbish.

The actual figure quoted could actually be correct depending on the context and test environment, but without knowing what was actually being discussed it means nothing. Why an expert would post up such who knows?

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Peter,

Any battery is at 100% DoD when the user declares that it is at his determination of acceptable end of discharge, or 'flat', wheresoever that may be. One person's definition of end-point may not be another's.

The graph I utilised does not prescribe a user arbitrated end point. It is an engineering representation of a battery behaviour when transiting between maximum acceptable charge and total discharge and is the appropriate way to represent it without user qualification appropriate to individual circumstance. As offered, it is the correct form to evaluate and express the available energy. I expect that it would be useful for anyone wishing to consider his battery management.

If it offends your senses as being one who routinely discharges his batteries below otherwise industry recommended values, then so be it. However it was offered to illustrate the diminishing available energy due to falling voltage, not to preach a philosophically better management practice. I would ask, whose definition is "100% DoD at 10.5v"?
In particular, the characterisation of specific criteria effects an explicit implementation of any discrete configuration mode. I'm sure you would appreciate that?

You may well consider it a "load of crap", particularly if you do not understand it, but I very much doubt that you are "sorry".

And Peter, as you always conclude your missives with your name, it would be courteous if you would address the recipient in your opening....... my name is Allan.

Alan,

Don't know about Peter, but my comments are regard a statement by another contributor earlier on and not your graph above. I assume your graph is comparing lead acid to Lithium whilst under going a heavy discharge and looks reasonable to me.

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Thanks for clarifying that Leigh. Your Followup was not making much sense to me and I was just composing a response when you posted again. Thank you. Have you re-posted it to the correct discussion point?

No, not a lead-acid versus lithium presentation. It was principally to quantify the 'diminishing returns' of pushing discharge beyond the 'nominal 50% DoD' in lead-acid batteries.
The presence of the Lithium curve on the graph was coincidental but it was useful to illustrate that my assertions did not apply to Lithium.

I see nothing 'wrong' with taking discharge below 50% if it suits the purposes of the user, but I believe that many do not appreciate the significant difference between Ampere-hours and Joules or Watt-hours. So I put up that post as information not as an argument relative to DoD advocacy but some may not have realised that!

Thanks for that and yes there are many ways to skin a cat depending on your needs.

Thanks Allan. Appreciate your help.

I have used this forum since the very early days and am well familiar with its nature and don’t visit so much these days. It was forever thus, tbf. Still, some great contributions and help for some of us with a limited grasp of the elusive foibles (to some of us) of batteries and 12v appliances.

Just to, clarify: accepting the nominal dod of 50% and 80%, there is possibly an extra gain of (around) a further 5% with lithium due to the late curvature drop-off as seen on the graph? (Nominally and theoretically of course)

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That's good Steve. Clearly you understand.

We generally talk of how "full" containers are so I'll express in SoC (State of Charge) rather than DoD. It makes more sense most times.

So a fully charged lead-acid AGM battery would exhibit 12.6v = 100%.
When it has fallen to 50% it would be about 12.06v with 40% =11.9v.
If it gets down to 0% you may still see about 10v but it probably won't deliver much energy!
So for battery health it is best not to go below 12.0v. If it ever gets down to 11.5v then it really needs to get on charge ASAP!

Now be very clear..... these voltages are being measured only after the battery has been resting for at least 30 minutes with absolutely no current going in or out. This is not really convenient for observation so for general monitoring, whilst the battery is discharging at say 10A you may expect to see 11.5v when it is down to 50% SoC. With the load removed this voltage will progressively rise to maybe 12.0v
So assessing battery SoC by voltage observation is not a very precise matter. But it may be all you have.
In the past, assessing by measuring the electrolyte specific gravity with a hydrometer was the norm but it was messy and with today's 'sealed' batteries, often impossible.

Because of their very flat voltage decay, lithium batteries are much more difficult to assess SoC by measuring voltage alone. So it is usual to use instrumentation to establish the 100% SoC by voltage measurement and current drop-off when on charge then integrating the current, both in and out to produce a SoC indication. However they still determine the low-limit by voltage and disconnect if need be to protect from disastrous over-discharge. Most lithium packs contain this instrumentation and protection internally. Additional monitoring displays can be added.
Similar instrumentation can be used for AGM batteries. Because of battery variables these systems may need to have their start-points reset from time-to-time.

But to answer your question..... apart from being able to discharge further, there is a distinct advantage with lithium that it can do so with much less voltage droop and thus deliver a better maintained supply and greater energy. Even down to the 50% point the lithium maintenance of voltage will enable delivery of maybe 10% more energy than AGM. From then on down to cut-off at about 20% you are way ahead of course. So theoretically, a lithium of say 50Ah rating will deliver about10% more energy than a 100Ah AGM limited to 50% discharge.
On top of that, the lithium does not suffer from energy losses brought about in AGM's as a result of what is known as the Peukert effect when discharging at higher currents. (but that's another story)
Weight, volume and life economy are also lithium features..... pity they are so expensive.

Cheers Allan.

Just been reading up on sodium batteries. Pity they’re not market-ready yet.

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Steve, I don't think that there will ever be an end to emerging battery technology. No sooner do you settle on a choice than something better appears on the horizon.