advice new agm battery

stoney123 · Senior Member

advice new agm battery

T1 Terry · Guru

Hi Peter, sad to hear about your lithium battery problems, what brand was it? To get the high discharge rate required from an AGM battery required to run an inverter big enough to run the appliances you have mentioned, you will need a big capacity battery. You will need to build it from either very big 6v batteries or 2v batteries, weight will be the big issue.
If you have enough solar you can run these appliances while the sun shines, that is the way Peter-n-Margaret do it in their OKA, but that is still a 400Ah battery.

T1 Terry

Jaahn · Guru

Hi Peter smile

I have used these battery suppliers. Reasonable quality at a reasonable price IMHO. Have a look around their site and see the current specials and also you can get information there and ask questions. I have no connection but recently bought a battery there again. wink Those 140Ahr AGMs looked good value to me on special with free freight. The carrier said gees that's heavy ! A good thing for a good LA battery.

Aussie Batteries & Solar . https://www.aussiebatteries.com.au/

It is hard to say how much Ahr you need, you do need to add it up as you use it, but the more the better. Perhaps your solar is a bit too small too for your usage. If you use more power than you generate regularly that will kill any battery including the new ones ! furious So you must always have more solar than you need to fully charge your LA batteries every day if possible. Do you monitor your batteries and usage and charging.

I just noticed you have an Engel fridge there too. That is a constant current draw 24/7. You need 2x140Ahr IMHO as a minimum to run the fridge and handle that 1500W inverter. The AGM batteries have flat top screw in terminals.

Jaahn

-- Edited by Jaahn on Tuesday 16th of July 2019 03:12:38 PM

Peter_n_Margaret · Guru

T1 Terry wrote:
If you have enough solar you can run these appliances while the sun shines, that is the way Peter-n-Margaret do it in their OKA, but that is still a 400Ah battery.

Not quite accurate Terry.

We can run any of our electrical appliances whether the sun is shining, or not, even though those 400Ahs of AGM batteries are well past their use by date now. It would be rare for us not to be able to crank up the diesel heater early in the morning and then run the electric jug to make the coffee, all before the sun provides any help. A recent trip into the desert saw us put 15L of diesel through the diesel heater for the central heating, the hot water service, and pre-heating the OKA engine.

But yes, running high power drawing appliances when the sun is shining certainly takes the load off them.

Cheers,

Peter

Whenarewethere · Guru

Birko DHS13 kettle is only 750 watts so a much more sensible load than most kettles. It is really well made & no plastic inside, only the lid. Its only disadvantage is that it plugs in.

They also make an 800ml kettle DHS8 also 750 watts but obviously more compact which might be more interesting for a caravan!

http://birko.com.au/index.php/catering/drink-heater

Peter_n_Margaret · Guru

We have been using the smaller Birko in the OKA for many years. I think it is 850W though, not the current 750W.
Cheers,
Peter

T1 Terry · Guru

Hi Peter (Peter-n-Margaret), the diesel heater doesn't use that much, but how many watts is the kettle? Do you think you could run the appliances Peter in the opening post is running from his 1500w inverter from 400Ah of AGM batteries? Not trying to have a go at you with this question, genuinely curious. The lithium battery probably would have run them at some early stage in the batteries life, but as Jaahn has already said, 400w of solar might be a bit under done if running all those appliances as well as the Engel fridge.

We just fitted a 250Ah Lifeline battery (really a 210Ah @ C20 rate) and upgraded the solar to 450w (and rewired to get it from the roof to the battery) on a Jayco Silverliner and the better half of the couple wanted to know if it would run a microwave. I said no but now you say you can run the jug etc in the morning, I might have given them wrong advice. We did fit a Victron 375 inverter so they could run small hand held kitchen appliances and charge phones etc but if you reckon it would support a bigger inverter to run the microwave, I'll pass on that info to them.

T1 Terry

Peter_n_Margaret · Guru

The diesel heater does draw higher currents for a short time during start up while heating the "glow plug" and ours has a self designed fan/radiator because I did not want the noise of the common commercial heat exchangers. Unfortunately it does not move quite enough air and the heater cycles off and restarts about every 30 minutes. Not ideal.

To answer your question Terry, our 9 1/2 year old AGMs would struggle to run anything over 1500W for more than a few minutes now, but when they were in better condition, they would have had no problem doing that.
But since the OPs inverter is just 1500W, then none of those appliances would likely draw much more than that anyhow, so yes, we could run them for a while even now.

Just a couple of weeks ago we were in the desert, the morning temperature was -2C, the diesel heater had been running for a couple of hours, one laptop, & 2 compressor fridges were running and we had already made the coffee using the 850W Birko to boil the water and Margaret chose to switch the fridge off and defrost it with her 1200W hair drier via the 1300W inverter.
The sun was not helping at all at that stage and I must say I was concerned, but I need not have worried. The house battery dropped quickly from 12.4V to 12.1V and then to 11.9V by the time she had finished, but it recovered very quickly and life went on.

So what to choose? Lithium or AGMs?
The lithiums will run those big draw items without nearly so much voltage sag, no question, and 400Ah of AGMs only needs to be replaced with about 200Ah of lithium for that application, as you continue to remind us.
Lithiums will also be considerably lighter which is a very attractive feature for many, including me.
Then there is the question of what happens when the sun does not shine. In those circumstances we can go into survival mode and eventually limit our electrical consumption to fridges, water pumps and a light.
In that mode our survival is about Ahrs. Voltage drop is not a question because none of the appliances draw more than a few amps, even if they all run together. An Ahr is an Ahr. It matters not what type of battery it comes from and in that case, 400Ah of AGMs can not be replaced with less than 400Ah of lithiums (or anything else).

So, when I replace our tired AGMs I will replace them with 400Ah of something, whether they be AGMs, Lithiums or something else.
I can buy 400Ah of AGMs for close to $1,000 (including freight) and history tells me that they will do us for 5 - 9 years.
What cost 400Ah of Lithiums? And how long will they last? I won't go there, but the calculation needs to be made and to include the 'loss of use" of the extra cash required.
Cheers,
Peter

-- Edited by Peter_n_Margaret on Tuesday 16th of July 2019 11:33:38 PM

T1 Terry · Guru

In your case Peter, I'd say stay with the AGM batteries. You have adapted to living with a limited store of energy and have had a very good life out of the AGM's, something very rare these days so it shows you very rarely use much more than 40% of the batteries capacity and you have the cabling set up in a way that all 4 batteries contribute evenly. You use your inverter judiciously and maybe rely a lot more on specialised low draw appliances and 12v appliances than the average RV owner entering the market now.
I doubt you would find many RV's with 460Ah of battery and 880w of solar, so you situation is a bit unique, not the norm by any account.
Trying to convince someone that a 1300w inverter is enough for there needs these days would be a very hard sell, even a 2000w inverter that can handle a50% over load for 5 mins is a bit of a hard sell these days. If mum can use the appliance at home she wants to take it with her when travelling or she considers travelling in an RV off grid is not much more advanced than camping in a tent. Fine for those that bounce from caravan park to caravan park, but to stay off grid all the time while travelling and set up some where for a few weeks at a time, the 460Ah of AGM batteries and a 1300w inverter would not produce the "happy wife, happy life" required for long term travelling for the majority these days.
In the case of the van I asking about with the 210Ah battery, that would require the 2000w at a min inverter to power the microwave. That would be a 180 amp draw, yes the battery could do it, but they certainly wouldn't get the 9+ yrs you have out of the battery.
For the equivalent useable capacity before the battery dropped below 12v under that amount of load, a lithium battery would have been $530 less than this Lifeline 210Ah battery, given a longer life and come in at roughly 1/3rd the weight. The reason this owner wanted to stay with an AGM battery "this isn't the van we plan to keep, we are new to caravan travelling so we will go with the technology that was installed by the manufacturer", "if we find we enjoy caravanning and free camping we will buy a van that we want to keep and get that set up with lithium batteries"

The OP for this thread wants to run an induction hot plate, that won't run from a 1500w inverter because they require 2200w each time they pulse on, so no idea how they are doing it now from the drop in lithium battery they had that died.

T1 Terry

Peter_n_Margaret · Guru

T1 Terry wrote:
You have adapted to living with a limited store of energy

I need to challenge that Terry.

I did think that you now understood the difference between power and energy, as this is exactly what caused many of the better electrically educated to criticize you in years gone past.

We actually have a larger store of energy than most and we use more electrical appliances than most, both "medium" draw and low draw and have done so for many years.

As I said in my previous post, 400Ah of AGMs (or any other battery) will run a compressor fridge for at least twice as long as 200Ah of Lithium. You need to acknowledge that.

Lithium batteries have some valuable features, but anything they can do can also be done with AGM batteries at a significantly lower up front cost. Whether Lithium will be cheaper in the long term or not is yet to be established and for it to be so, there can be no "accidents" like the OP has encountered.

I know you will need to have the final word.

Cheers,

Peter

El Gringo · Senior Member

I don't usually add much to these discussions, mainly because my knowledge is extremely limited at best.

However I would like to ask you Peter about the energy storage.
Obviously Ah's are Ah's so 400 is twice 200 regardless of the means of storage.
But doesn't the ability to redraw that storage come into the equation?
Isn't it more about usable storage?

The accepted usable rates that I'm aware of are 50% usable for AGM and 80% usable for Lithium
Which would mean your 400Ah AGM can return 200Ah of usable storage, and 200Ah of Lithium would give 160Ah of usable storage.

I see it as being like a fuel tank with the pickup from the tank set at either 1/2 way down or 80% down.
Making it possible to draw only that amount of energy from the tank.

This is always the way I have seen it, so am I looking at it wrong?

Also, how low a charge do you allow your batteries to go?
Is the 50% thing something you have stuck to or do you have a different regime?

Thanx,
Bernie

Whenarewethere · Guru

I think one first needs to know precisely how much energy the heavy load items use.

The induction cooker's average maybe ok but when it cycles on as mentioned above, it is 2200 watts.

Toaster probably 800 watts.

The kettle can easily be replaced with a 750 watt model. 200ml of water from 16°C to boiling 120 seconds, 110 seconds would be good enough, & if it is for coffee 100 seconds is plenty. Never use boiling water in coffee, & you save some resources as well!

Sandwich cooker I don't know what these use.

Can one use the induction cooker only while there is plenty of solar as that will take a substantial load off the battery.

Are you actually getting everything out of the solar panels with proper wiring.

& as mentioned how much energy reserve do you need to run the fridge.

I think once you have some peak & average figures at the consumption end then you can get the right capacity battery.

Also is the wiring to the inverter heavy enough. I have been buying wire while other people were buying wire for inverters, both well under size, I made a few comments on resistance, the response was, it will be ok. Frightening stuff!

Whenarewethere · Guru

If you have more AH & you are only running a fridge in an emergency you can run it down as far as you can.

You probably only do this once or twice a year so in the scheme of things it is not a big hit on the overall life of the battery.

99% of the time one is probably only using 20% a day so I would not worry draining the batteries on the odd occasion. The more AH the better.

That's how I use my small setup.

T1 Terry · Guru

Rather than dragging this thread off topic too far, I'll start another thread regarding battery Ah, how it's measured and the relevance etc an Ah is not necessarily an Ah when it comes to advertised battery capacity

T1 Terry

Peter_n_Margaret · Guru

El Gringo wrote:
I don't usually add much to these discussions, mainly because my knowledge is extremely limited at best.

However I would like to ask you Peter about the energy storage.
Obviously Ah's are Ah's so 400 is twice 200 regardless of the means of storage.
But doesn't the ability to redraw that storage come into the equation?
Isn't it more about usable storage?

The accepted usable rates that I'm aware of are 50% usable for AGM and 80% usable for Lithium
Which would mean your 400Ah AGM can return 200Ah of usable storage, and 200Ah of Lithium would give 160Ah of usable storage.

I see it as being like a fuel tank with the pickup from the tank set at either 1/2 way down or 80% down.
Making it possible to draw only that amount of energy from the tank.

This is always the way I have seen it, so am I looking at it wrong?

Also, how low a charge do you allow your batteries to go?
Is the 50% thing something you have stuck to or do you have a different regime?

Thanx,
Bernie

Bernie, a 400Ah (name plate) AGM can deliver 400Ah. They can be charged to the full 100% and discharged to zero (10.5V). In fact, if the discharge rate is low, like just running a fridge, lights etc, it will actually deliver more than 400Ah which is typically the quoted 20Hr discharge rate.

It is a false but commonly held view that running AGMs (or other LA batteries) down to very low state of charge significantly reduces their life. It does, but only by a very minor amount. Yes, the number of full cycles that the battery will deliver reduces significantly with very deep discharges, but battery life should be measured in energy delivered over its total life, not by the number of discharges. A discharge to 100% delivers double the energy compared to a discharge to 50%. Most people seem to never recognise that. If you check the data supplied by any manufacturer and convert it to Ah delivered over the life of the battery, this will become clear.

Lithium on the other hand promises significantly longer life, both in cycles and in total power delivered, but those promises are still promises and they come at a considerable monetary cost. If you calculate the Ah delivery of a 400Ah lithium bank you will find that the "experts" recommend charging to 90% maximum and cease discharging at 20%. There are damage risks going beyond those limits without great care and attention. This means that a nameplate 400Ah bank of lithiums will only deliver a nominal 280Ah. That is a big reduction compared to the same nominal capacity of AGMs. Very low discharge rates will increase that too, but I am unsure by how much.

Don't get this wrong. I am not anti lithium at all, but some of the claims tend to make them into something that they are not. I have been considering getting rid of our gas cooking which is the last gas we have in use. To do that I would prefer a 3 plate induction cook top plus a convection microwave. Restricting use to one plate at a time would never work for the cook, so it would require an additional much larger inverter and a 400Ah bank of Lithiums and more solar would be a no brainer. I would need to go lithium for the weight reduction as well as the power delivery rate. But the cost of that would be pretty scary.

In practice, we rarely discharge our AGMs below 50%, but I can and will at any time that we need to without fear that they will suffer as a result. Having a buffer for several days of bad weather is important for us, but frankly, adding lots more solar is cheaper than adding batteries and that is my recommendation to most people. More solar makes bad days less bad they are cheaper than batteries and they will certainly last longer too. It has been full cloud cover with occasional drizzle all day here today, but we still had charge rates of 6A for most of the day.

Cheers,

Peter

El Gringo · Senior Member

Thanx for your reply Peter,

Definitely agree with the priority for solar, whole roof covered is our intention, will net a bit over 3Kw.

However you seem on the one hand to ignore the "experts" warning for the AGM's but wanting to heed those for the Lithiums?
Whilst I don't doubt that you have taken yours to a low state of charge, I really doubt you have taken them to empty?
And from what I have read taking them to 0 drastically reduces their lifespan.

With the lithium's I can't see where the recommendations are to under charge them,
As far as I am aware 3.6v per cell is fully charged for the Winston cells and with T1's system that is where the charge cutoff is.
Perhaps you are referring to these drop-in replacements? Though some of them seem to go for insanely high cutoff's too?
I am also aware of occasions where cells have been fully and completely discharged without any apparent significant damage resulting.

So I think in real terms the usage of the batteries will usually be at about the 50% mark for either type, but with an easy 25% extra available with Lithium for emergencies without fear of any issues.

Yes cost is the big hurdle.
For me like everyone else it come down to a perceived benefit vs cost exercise.
This will be different for pretty much everybody.

For me and my wife, our bus is our only home, we have no real estate to fall back on and as we get older we don't want to worry so much about replacement costs.
With the perceived benefits for us being, capacity usable, rate of charging, rate of discharge (at a constant voltage) - yes we want and have A/C's and intend to use them.
The lower weight doesn't factor in so much as a 15t bus we have capacity for either, but less is always better as I'm sure you would agree.
Yes it is a very large outlay, biggest of the budget overall, but we are saving for it and hope to get Lithiums installed in the not too distant future.

Cheers,
Bernie

Peter_n_Margaret · Guru

Bernie, I am happy for Terry to address the questions of practical SOC limits for the Lithiums and would accept his view, but I stand by my comments on AGMs, views which are well supported by manufacturer's data.
It is also interesting to note that Lithiums also "suffer" from voltage drop under high loads, but not to the same extent as AGMs and other LAs.
Cheers,
Peter

Tony Bev · Guru

Hi Peter (stoney 123)

I shall try and answer this part of your question
b) I intend to just unplug lithium and connect agm however the wiring is all set up for a battery with 2 posts which has a screw on cap so with an AGM how do you keep all the connections on each post in place? A rubber chair stopper?

If I have interpreted the question correctly, then the answer is

You can purchase the following type of battery terminals, (depending which ones you require), from any auto store, (or they could order them in)

Hope that this info is useful

stoney123 · Senior Member

cheers terry,

got big inverter (although) have to turn induction cooker to low when turning it on, but low on induction boils water very quickly. :

stoney123 · Senior Member

tks, just had a quick look at our link. they look ok. you are right in better to get 140AH + as you should only use 50% to keep battery in health.

one will do for engel, phone and laptop. get the 2nd battery when get a trifecta :)

cheers

stoney123 · Senior Member

tks tezza,

deisel heater....lucky you.. i am tenting.. but when i get two batteries i can run the electric blanket thingy next winter :)

stoney123 · Senior Member

GURU spot on !!!

now i have to check that existing wiring will allow for the wide posts in AGM, with lithium the posts are close

-- Edited by stoney123 on Tuesday 30th of July 2019 11:56:19 AM

stoney123 · Senior Member

the induction on low uses about 800 watts and boils very quickly, tks for the tip though. I have to watch weight and clutter. I am messy :(

T1 Terry · Guru

Electric blanket uses very little power and as long as it isn't one of those high tech ones that tries to maintain a temp rather than the 3 position and off controller type, you can get away with a modified sine wave inverter as well.
Having said that, the Victron 375kva PSW inverter is fairly cheap, will run the electric blankets as well as phone chargers etc yet has a very low overhead loss and drops to almost zero draw when there is no load.

Can you tell use what brand the lithium battery that passed away was? Better the members here know what to avoid rather than suffer the same problems you have had. What did the seller say when you reported the battery had died?

No idea what area you are in, but we are in Mannum SA and I'd be interested in buying the dead lithium battery off you so I can have a look and see how they were built and just what failed.

T1 Terry

Brenda and Alan · Guru

Stoney would i be right in thinking that you do not have a way of monitoring your batteries voltage during use. If this is the case then any type of replacement may suffer the same fate as the previous one.

Alan

-- Edited by Brenda and Alan on Thursday 1st of August 2019 06:14:40 PM

Aus-Kiwi · Guru

We went through batteries every 2 or 3 years . Since doubling the solar and AH of batteries . Weve passed 5 years and no issues so far . All going well ! But Ill kinks myself now !! Lol Does anyone share the motor batteries down to say 12.7 volts ? Via VSR . I find this helps keep both battery packs charged . 600 AH all up .

Ellynsteve · Member

I imagined that lithium batteries are fairly recent additions to Rvs, so surprised to hear yours have died, can I ask how old they are? We have 1.8 kwatts of solar on the roof and 500Ahs of AGM batteries, and find the system drops significantly over night running a 200 litre compressor fridge, tv, water pump...and bounces back usually by about 10am.

stoney123 · Senior Member

18 months. it just has 0 charge, even though have had no load. I have a victron battery monitor but its screen is blank. Have ordered an AGM will connect the victron and see if it works.

Will try and ressurrect lithium it was bloody expensive.

Tony LEE · Guru

Seem to recall Collyn saying that a strict lower limit of 50% SOC for decent AGMs was just as much a myth as being able to run lithiums from 0 to 100% forever. As well as the factors Peter has already explained, the limiting factor of any solar system is where is the energy going to come from. To tweak Peter's point a little further, the type of battery is irrelevant if it is empty and there is nothing to recharge it.

T1 Terry · Guru

Hmmm...... interesting Collyn spruiking any knowledge about lithium, besides what anyone can read on the interweb.
The first thing anyone who knows much about lithium batteries is defining the 0 part. If it is 0% SOC, then that point needs a reference to the load used to discharge the battery from 100% to 0% SOC and over what time frame. 0V is not something that can occur in a lithium battery with a fully connected circuit as the cells actually produce a voltage while consuming their internal structure. This produces a lot of heat, enough to melt plastic and burn through cables. Without actually stating what the "0" meant, anything otherwise stated doesn't actually mean anything much at all.
The same goes for the "50% SOC of an AGM battery, what was the capacity at 100% SOC allowing for deterioration due to age and/or abuse so half of that cold be determined. At what load was the 50% drawn off, C20, C100, C1, they will each give a different amount of energy available down to a set cell voltage, but if you can't access the individual cells then how do you determine the cell voltage for the claimed 50% SOC. Any battery capacity is limited to the weakest cell, we all know that yet never factor it into our thinking when considering the state of charge. 100%, 50%, 0%, they all really on the loaded voltage of the weakest cell.

I'd be very interested to perform a test on this "dead" lithium battery to determine if and why it is "dead"., More likely it simply has a failed component in the internal BMS, a failed connection or a failed cell. Very unlikely the whole battery has failed, so very unlikely it couldn't be resurrected from the grave.
It's all about knowing what you are looking at when you open the lid, if the technician knows little about lithium batteries then the chances of a reliable repair is about as likely as a kid pulling a wind up clock apart. Lots of bits and not real sure just what they are looking at, makes it very hard to diagnose what has failed to cause the problem. Easy enough to find the resulting damage, but that doesn't lead to rectifying the root cause, so the problem will simply repeat resulting in similar component failure, if the whole thing can get put back in the container in the first place of course.

T1 Terry

-- Edited by T1 Terry on Saturday 24th of August 2019 12:46:53 PM