Deep cell batteries

Tatah · Newbie

Deep cell batteries

Phil C · Guru

Hi and welcome to the forum

AGM or deep cycle batteries are an advance on the old lead acid car batteries.

Most caravans have between 100AH or banks of parallel batteries to increase the capacity.

We have 2 110AH batteries charged by the 240V mains and solar.

A fact that took me a long time to understand was that these batteries will have a much shorter life if discharged below 50% of rated AH capacity. When we free camp we can watch TV, have the lights on and electric blankets via an inverter and not cause damage.

There are a lot of technical facts that will only muddy the waters for you, so rules of thumb..

1. Make sure batteries have plenty of ventilation
2. If you have a device to measure the voltage of a battery don't let it go below 10.7 volts (about 50%)
3. Make sure the batteries get a full charge during the day, we hook up the generator if the voltage is below 13.5 volts at 4PM
4. As part of van electrical maintenance, make sure the terminals are tight and there is no white/green crystals forming on the terminals.

Hope this is helpful, please private message me or any of the tech gurus if in doubt.
Cheers

Dougwe · Chief one feather

Welcome to the gang Tatah, enjoy here and out in the playground.

I will leave you sort through Phil's comments.

Keep Safe out there.

Baz421 · Guru

http://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

Here's some good reading if new to this subject.

IF YOU WANT AGM BATTERIES TO LAST DON'T DISCHARGE BELOW 12V.

At 12v the State of Charge (SOC) is 50% (roughly) - see the link above and the attached file table 7 and the chart below (so 3 sources of info say 12V approx.).

Our last set of 4 X 100ah house batteries lasted over 7 years (except 1 and that took an unnecessary load from the inverter because the sparky wired it wrong initially)

Battery test chart cropped.jpg

Baz421 · Guru

Here's another one easy to see in colour Tatah

AGM Battery SOC.png

Woody n Sue · Guru

And it's welcome from us two 2
Umm no comment on this from me as I am but a learner myself
Want to know more do what I try to remember to do before I post is use the search button up top in the middle of the page it don't really look like a button but it is
Enjoy as you learn from some very clever people's on here.
Woody

Phil C · Guru

Hi again,

There is that much confusion in these batteries as to what voltage is 50%. I do remember reading 10.7 volts someplace but the tables above only muddy the waters more.

So our poor OP plus this tech (me) are still in no mans land.. As I have said this is new technology to me, a battery was flat when the SG went lower than a fixed measure (I think it was 1150).

Anyway, if anyone can come up with a definitive voltage that makes sense, Im sorry 12.06 and 12.2 volts just doesn't make sense when the terminal voltage is allegedly 12 volts... Please correct me if that statement seems wrong, I hope you can see where Im coming from. Perhaps we all need to research this some more.

Image result for 12 volt battery specifications This will only muddy the water even more.. I may have been reading on load terminal voltage... can open, worms all over the place... this table came from a agm battery manufacturer, sorry guys

Cheers

-- Edited by Phil C on Friday 17th of July 2015 09:19:41 PM

Jaahn · Guru

Phil C wrote:
Hi again,
There is that much confusion in these batteries as to what voltage is 50%. I do remember reading 10.7 volts someplace but the tables above only muddy the waters more.
So our poor OP plus this tech (me) are still in no mans land.. As I have said this is new technology to me, a battery was flat when the SG went lower than a fixed measure (I think it was 1150).
Anyway, if anyone can come up with a definitive voltage that makes sense, Im sorry 12.06 and 12.2 volts just doesn't make sense when the terminal voltage is allegedly 12 volts... Please correct me if that statement seems wrong, I hope you can see where Im coming from. Perhaps we all need to research this some more.
This will only muddy the water even more.. I may have been reading on load terminal voltage... can open, worms all over the place... this table came from a agm battery manufacturer, sorry guys
Cheers
-- Edited by Phil C on Friday 17th of July 2015 09:19:41 PM

Hi,

Well there is no definitive way to tell the state of charge of a battery by just measuring the voltage unless you leave it to 'rest' for some hours. AND the different types of battery have slightly different voltages. So that is why it is confusing. AND the 12 volts is just a nominal voltage anyway so just forget that figure for an accurate reading. confuse

The voltage drops the moment the current is taken out and the heavier the load, the more the voltage drops, but when the load is taken off the battery voltage comes back up. So that is why the battery needs to rest for an accurate reading. As was mentioned in the 'old days' you took a SG reading of the acid to know the state of charge, but that is not for today. hmm

If you want to really know then you need a charge controller or total meter which reads the current going in and the current going out and tells you how much you have left. Simple really. Or you can use a voltage meter and observe the readings under your normal loads to get a 'feel' for how the voltage should be as the current is used up. That's what I do. biggrin

That voltage chart by BAZ421 looks good to me and is about the right voltages in my experience. Your chart above is crap Phil C and should be ignored !!!!! Ordinary lead acid batteries and gel batteries drop the voltage more under load than AGM batteries in my experience so that has to be factored in. hmm However below 11.5 volts is living dangerously depending on the load so relying on some cutoff voltages in appliances is not wise as they are usually set too low for long term battery health.

I hope this helps a bit.Jaahn

-- Edited by Jaahn on Saturday 18th of July 2015 08:31:09 AM

TheHeaths · Veteran Member

I can't understand what the OP wants.

Do they want a guide to good batteries, a guide to those that last the longest, a guide to best aH per dollar available or do they want the kind of in depth tech information that the good people of this forum are starting to provide.

It would be good to get a bit more of a pleasant request and guide when people post.

I am sorry, but I wouldn't answer anyone if they asked me for something in this manner, and we see so many requests for information made in this way.

Phil C · Guru

Cheers folks

Jaahn is correct in saying my little table (taken from a manufacturers web site) is wrong.

In days gone by, you would measure a battery voltage under load to get an accurate picture of where the SOC is. Im convinced that now days its a guessing game as there is no hard and fast rule (as far as I can see).

I agree the OP has gone AWOL on this one as well, I was rather hoping that there would be some response, it has however opened a good discussion on these new batteries which I confess, I still have little knowledge of.

Im very much of the opinion that its suck it and see. The trouble is, that in my caravan the batteries are never at rest due to the charger/conditioner activity, I am concerned now that under load (TV, lights and inverter at low DC amps) the voltage gets below 11 volts. Should I ignore this? My setup is rather robust as it is 2 100AH batteries in parallel. In the above example Im drawing around 7 amps. The device I have to measure is a SETEC drifter panel. Mind you, if I shed the load the voltage bounces back to over 13 volts.

Hopefully somebody can help me clear the mist.
Cheers

Baz421 · Guru

Phil C wrote:
Cheers folks

Jaahn is correct in saying my little table (taken from a manufacturers web site) is wrong.

In days gone by, you would measure a battery voltage under load to get an accurate picture of where the SOC is. Im convinced that now days its a guessing game as there is no hard and fast rule (as far as I can see).

I agree the OP has gone AWOL on this one as well, I was rather hoping that there would be some response, it has however opened a good discussion on these new batteries which I confess, I still have little knowledge of.

Im very much of the opinion that its suck it and see. The trouble is, that in my caravan the batteries are never at rest due to the charger/conditioner activity, I am concerned now that under load (TV, lights and inverter at low DC amps) the voltage gets below 11 volts. Should I ignore this? My setup is rather robust as it is 2 100AH batteries in parallel. In the above example Im drawing around 7 amps. The device I have to measure is a SETEC drifter panel. Mind you, if I shed the load the voltage bounces back to over 13 volts.

Hopefully somebody can help me clear the mist.
Cheers

Phil Batteries are far more advanced than when were RAAFies in 70's that's for sure.

However as to your question above - I never let ours go below 12V under load, NEVER. By the way they sit on 12.2V down to 12.1V down to 12.0V for ages and ages, UNDER LOAD. As I said our last lot of 4 X 100ah batteries lasted 7 years except one which was connected to an inverter wrongly by the sparkie who wired the van at manufacture.

That one battery obviously went below 12V without me knowing it until I looked very closely at the wiring and that battery lasted 2 years.

One thing with AGM's make sure they are fully charged and charge at the 20ah rate (for your own batteries - should be printed on the battery) for a while to see how they come up, ie if they come up quickly in say 6 hours or so they were not flat at all BUT if they take 24 hours to charge they could reasonably be called flat.

You get a feel for it if you watch the amps IN ie solar on fine day for us is 25A if batteries low for say 6 hours before charge rate drops to float voltage. So in that 6 hours I put back say 150Ah from a bank of 400ah batteries. So I have not even taken the batteries down to 50% of capacity (not SOC here).

Hope this helps.

Cheers Baz

Jaahn · Guru

Tatah wrote:
Need advise on cell batteries with the longest amp hours

Hi Tatah,

We are not sure exactly what you are asking for. Please look at the replys and ask again for some more directed answer. wink

However a general reply is this. You must buy a DEEP CYCLE type of battery not just an ordinary car battery for using in the caravan or motorhome to run the house. There are several types of these, lead acid, AGM, gel. The price goes up a bit for each type and they get a bit better and give extra life. That's just speaking generally, they all work well.

However the size of the battery is the big decision to make. This is the AMP HOUR capacity. Ratings of 100 AH, 150 AH, 200 AH, and up are common. Two or more can be linked together to get more capacity also. The bigger the capacity the longer you can go without charging them, BUT you have to charge them again some time and how to do this is just as important to consider. confuse

Note these are usually all 12 VOLTS. Or two x 6 VOLTS linked together or if you have a truck you may link two 12 VOLT batteries to get 24 Volts because the truck has this voltage. However the voltage must suit the lights and fridge and other things you are using in the van. Usually all 12 volts is the most common. smile

Hope this help some other people too !

Jaahn

Phil C · Guru

Thanks Bazz, I have the feeling that if I put my multimeter on the battery direct I would get a different reading than the drifter. OK maybe I have let them get too low, only time will tell. Mind you, my pocket won't be pleased if they are naffed.

Fingers crossed
Cheers