Is it wise to allow Deep Cycle Batteries to always charge?

Hi Everyone
Firstly, thanks for the huge amount of informative information on this site, it has proven to be quite useful.

Unfortunately, due to the large number of Deep Cycle battery related posts, I cannot find an answer to the following.

My 4x4 is a daily driver, used for work also.
I have a 105 AGM a/h deep cycle bat for camping etc.
This is charged from the vehicle alternator via a 100 amp solenoid and timer set for 2 mins after start up, and 120 watt panel when camping.
When driving about daily, the only current draw from this battery is the LED interior lights and my small Waeco 15 litre lunch fridge (occasionally).
There is a designated Analogue Volt gauge for the Aux bat which I monitor to ensure my timer (for aux charge system) still works.

I was thinking that this deep cycle battery should be allowed to discharge and then recharge occasionally rather then being kept topped up always.

To do this, I will install an isolation switch for the solenoid and mount it next to volt meter. Then simply turn this on when voltage drops as required.

Given that I am finding so many knowledgeable folk on this site, I am interested in reading what the thoughts are.

Should I allow the battery to drop in voltage, NOT allowed to be flat offcourse, and then re-charge.

Thanks once again.
Dave

PS.
I am thinking of posting a drawing with parts and details of how I have set my vehicle up for the purpose of sharing what I have done.
Please advise me what section I am best to do this, and how.
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Reply By: Mick O - Saturday, Feb 16, 2013 at 11:04

Saturday, Feb 16, 2013 at 11:04
That's an interesting topic Dave. I'm carrying 2 x 140 A/H AGM's in the back of the tuck truck and by and large, the vehicle sits in the driveway between trips. I think the lowest the batteries have ever been may have been around 75% of capacity. Certainly in the driveway, with 300W of solar feeding in, they are in float mode at 100% capacity the majority of the time. They are administered by a Redarc BMS battery charging system.

I've always presumed that being an AGM battery and designed for long periods of storage at high capacity or float for use in emergency /security systems etc, they would be OK.

It does pose the question as to whether the batteries would benefit from a significant draw down to say 60% every now and then or is standard use for me (never much below 90%) and immediately topped up again going to ensure the batteries remain in tip top condition.

At a significant investment cost, I hope I've been treating them right.

Hopefully someone with a bit of battery expertise will be along momentarily to offer some advice (hopefully not polarising the responses though ;-)

Cheers Mick
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trip would doubtless be attended with much hardship.''
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Reply By: pop2jocem - Saturday, Feb 16, 2013 at 11:05

Saturday, Feb 16, 2013 at 11:05
Hi Rimbus,

I have a similar set up in my Cruiser ute. The auxiliary 100 AH AGM in my case is charged through a "smart relay" not sure the brand, Matson I think. As you probably know this relay cuts in when the cranking batteries charge gets to 13.6 or thereabout volts after start up and opens the charging circuit to the AGM when the cranking batteries voltage drops to about 12.8 volts after shut down. I have a 40lt Engel that lives in the ute more or less permanently but only gets switched on when we go away. This is connected to the AGM. In my case this battery gets topped up every time my ute gets started and driven so I guess it never gets discharged except for when we go away and the fridge is left on while the engine is not running, usually over night.
I have had this battery and set up for about 4 years so far and the AGM seems to work fine when needed. I made a similar inquiry as you when I set mine up and basically was told that the best way to get a long life from any battery was to keep them charged up and not let the voltage drop below 50% charge when being used 12.2 volts I think.
Hope this helps

Cheers
Pop
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Follow Up By: daz (SA) - Saturday, Feb 16, 2013 at 11:17

Saturday, Feb 16, 2013 at 11:17
Hi Rimbus,

I have always been told that there is no benefit in allowing batteries to partially discharge.
The advice I have been given is to keep a battery at full charge whenever possible.

Daz
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Reply By: Gronk - Saturday, Feb 16, 2013 at 11:12

Saturday, Feb 16, 2013 at 11:12
Batteries don't really like being discharged !!!!!!
Now we know that's what they get when we use them, but when not being used.....keep them fully charged..
Discharge them....then recharge ?? no.....no need and no point ..
Standby batteries usually have a long lifespan because they are always fully charged ( float ) and usually never get used.....
AnswerID: 504857

Reply By: fisho64 - Saturday, Feb 16, 2013 at 11:42

Saturday, Feb 16, 2013 at 11:42
you may be getting confused with Ni-Cad batteries, which have a memory. If you constantly cycle a nicad to (say) 70% after a while it believes that is the low point and capacity is reduced.
There are various methods around to reinstate this, some dubious.

But lead acid batteries and their variants deteriorate while discharged so are better left fully charged rather than cycled for the sake of cycling.
AnswerID: 504858

Reply By: Member - bungarra (WA) - Saturday, Feb 16, 2013 at 12:19

Saturday, Feb 16, 2013 at 12:19
Hi Dave

My set up is 2 x 105 Ah AGM deep cycle connected to the alternator via auto isolator and as well to a solar panel....in the vehicle used for run a round and fridges etc when away...........The batteries never run down and have probably never gone below 80%.

Into their 9th year of service..........good quality batteries to start with..........so I guess that gives you an answer of sorts..........

cheers
Graeme
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Follow Up By: Member - bungarra (WA) - Saturday, Feb 16, 2013 at 12:22

Saturday, Feb 16, 2013 at 12:22
PS .......those batteries were in for 4 years in my camper trailer under the same management system type......and I simply transfered them to the 'cruiser when I set that up.........hence the years to date
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Follow Up By: Rimbus - Saturday, Feb 16, 2013 at 21:14

Saturday, Feb 16, 2013 at 21:14
It is nice to know that if I take care, I can get that sort of life out of the $350 I just spent on a new AGM.
Cheers Graeme
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Follow Up By: fisho64 - Monday, Feb 18, 2013 at 02:25

Monday, Feb 18, 2013 at 02:25
might be a silly question, but if they have "never gone below 80%", how do you know what capacity they retain?
Im not an AGM expert but on conventional LA batteries voltage is only an indicator of the state of charge, not the actual capacity so Im curious how it can be measured otherwise?
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Reply By: Allan B (Member, SunCoast) - Saturday, Feb 16, 2013 at 13:56

Saturday, Feb 16, 2013 at 13:56
There are countless websites relating to batteries. On some aspects they will vary in their information but on one subject they are mostly in agreement..... With lead-acid batteries, whether flooded (cranking) or deepcycle (AGM etc), best practice is to maintain them in a fully-charged state at all times and to never leave them stand in a discharged state for more time than necessary. If connected to a vehicle alternator this will be achieved automatically. If left standing in say a caravan, best to be constantly connected to a mains charger with 'Float' mode.

I have found one specialist who suggests that some regular cycling extends battery life but does not support this with any evidence or reasoning. So there is no established benefit in 'cycling' a lead-acid battery as there can be for a Ni-Cad battery.

All lead-acid batteries will exhibit some self-discharge and if left without charge for enough time will discharge to a low voltage and permanent damage can occur to the cells.

So to respond to the original question, there is no need to 'cycle' the battery charge, but if it makes you feel better about being in control, it will do no harm to do so provided that the battery is not left for a time in a discharged state.

Cheers
Allan

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Reply By: Kris and Kev - Saturday, Feb 16, 2013 at 16:13

Saturday, Feb 16, 2013 at 16:13
I just replaced my car’s second battery with a Trojan 115 deep cycle. It is mainly to run our fridge in the car. Bought it from Battery World and the guy there asked how often we run the fridge. He asked because he said it is good for the battery if it is used occasionally.
I also know an electronics technician who was a shortwave radio nut and I remember him telling me that he gets a very long life out of his car battery because he runs his radios all the time.
So it is interesting that there are many different opinions.
Kevin
AnswerID: 504872

Follow Up By: Gronk - Saturday, Feb 16, 2013 at 20:19

Saturday, Feb 16, 2013 at 20:19
Different opinions ???

Nothing wrong with an opinion....but especially from a battery place....it shows how some have not got the expertise to know their product properly.....don't forget, they are mostly just salemen's.!!

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Reply By: member - mazcan - Saturday, Feb 16, 2013 at 18:20

Saturday, Feb 16, 2013 at 18:20
hi all
my deep cycle battery is 5yrs old and has always been charged by a 12w solar panel via a regulator while in the shed and is as good as the day i bought it
my original mazda battery died at age 8 after been trickle fed all its life by a 4w solar panel -----without a regulator ----- so i have proved beyond doubt that is the way to treat batteries no matter what they are for
4wd /camper/caravan usei also connect a solar panel to my vw golf when im not driving it via a regulator i been using solar for 20yrs
cheers
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Reply By: The Bantam - Saturday, Feb 16, 2013 at 18:30

Saturday, Feb 16, 2013 at 18:30
As has already been stated, all variants of lead acid technology should not be left in a discharged state for any longer than necessary.....if discharged should be fully recharged at the earliest opportunity and from any state of discharge.

There is no benifit to allowing a battery self discharge to a point that requires recharging.

There may be benifit...from a managment point of view....to leave a battery off charge for a period and monitor its terminal voltage, to see how much it is self discharging.........with a view to assessing its possible performence and life.
The battery should drop from the "charged voltage" to a "resting voltage" and hold that for some time.......if the resting voltage drops faster than it should. replacement should be considered.

If a battery is properly managed...either float charged or on a charger providing active managment there is no problem leaving the battery on charge indefinitely.
There are many systems, where the batteries are on charge at all times appart from when they must supply the load...these batteries last a very long time.


It can be argued that lead acid batteries can benifit from a strong discharge followed by a strong charge from time to time.....this is considered to reduce sulphation, because it produces vigorous chemical activity on the surface of the plates.

the benifit is not from being in a state of discharge but from the vigorous activity......start batteries get this every time you hit the key.


The idea of this charge and discharge improving the battery performance V's the additional cycles reducing the life of the battery must be considered......I have not seen any figures or graphs on this argument....as long as it is infrequent and not a deep discharge it can not hurt.

If you are going camping every 3 or 4 weeks, that should be sufficient in my mind.......if not hooking ip a spotlihght for 10 or 15 minutes every 4 to 6 weeks or so wont hurt and may produce "some benifit"

Consider that you fridge will be far happier if it is run regularly...so turning the fridge on and running it overnight and then taking a good drive may be a good idea all round.

Maybe its a good reason for a day trip.

cheers
AnswerID: 504881

Follow Up By: Rimbus - Saturday, Feb 16, 2013 at 21:10

Saturday, Feb 16, 2013 at 21:10
Thanks for the detailed reply Bantam.
I typicaly start the big trailblazer up a day before on mains, swap to 12v when pulling out the driveway, adjust the temp occasionaly and turn it off for the clean out when home again.
I consider it to be less load this way, compressor is not having to pull compartment down for high temps in the morning.
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Reply By: Rimbus - Saturday, Feb 16, 2013 at 21:06

Saturday, Feb 16, 2013 at 21:06
Thanks everyone, much appreciated.
I agree with the idea of keeping the batteries charged up, I am just eliminating what "They say", you know the experts on everything who have no knowledge of anything……

Thanks to all the great info I have found here, I am confident my new solar panels will keep up with the 100 litre trail blazer and hand full of LED’s when tracking decent sunlight for the types of trips were doing presently.

The best bit is, I don't have to pull out the batteries, glove box, stero, fuel gauge housing thingy. Dismantle the split tube to run another single earth lead for a switch and put it all back together again.
AnswerID: 504887

Reply By: Honky - Saturday, Feb 16, 2013 at 21:43

Saturday, Feb 16, 2013 at 21:43
Had two 6 volt trojan 105's in my camper trailer.
Totally neglected and run nearly dry more than once, left discharged for long periods, overcharged to the point of swelling the casings and after after 9 years they are now completely stuffed.
Maybe I should have left of the charger.

Honky
AnswerID: 504892

Reply By: anglepole - Sunday, Feb 17, 2013 at 13:36

Sunday, Feb 17, 2013 at 13:36
Hi Ribus,

This is a promo video but has some interesting info.

http://www.youtube.com/watch/?v=m_P6IiL1qnU

Cheers
AnswerID: 504932

Follow Up By: Rimbus - Sunday, Feb 17, 2013 at 15:29

Sunday, Feb 17, 2013 at 15:29
Promotional – Yes
Interesting – Sort of
Informative – No.
It would be nice if these types of videos gave the specifics of why the alternative charging systems do not work, rather then dumbed down promo shine.
This is nothing against the Redarc products, I am using the TIM 06 timer myself.
It is against these types of videos and the lack of real information.
Thanks for sharing this though, nothing against your good self.
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Reply By: Dennis Ellery - Sunday, Feb 17, 2013 at 13:39

Sunday, Feb 17, 2013 at 13:39
It depends on your cycle history.
Lifeline Batteries advise for their deep cycle AGM - that if you shallow discharge your battery often - the battery capacity will walk down.
If you are working your battery lightly - it will pay you to give it a reasonable discharge occasionally.
AnswerID: 504933

Reply By: Member - John and Val - Sunday, Feb 17, 2013 at 18:02

Sunday, Feb 17, 2013 at 18:02
There's a lot of good advice above.

Something that hasn't been mentioned -

Batteries can suffer if OVERCHARGED. A multistage charger, either mains powered or a dc-dc charger, will basicly provide three charging regimes. Starting with a battery that is not fully charged, it will deliver a bulk charge at roughly constant current until the battery voltage rises to some preset value. Then the charging voltage is held constant and the current declines as the electrolyte reagents are used up. Once the charger senses that the charging current has dropped to a very low value (reagents virtually all used up) it changes into float mode, and maintains just enough voltage to deliver a small current to the battery, ideally just enough to replace what's lost through self discharge.

BUT - where a dc-dc charger is fitted to the vehicle, it will start up every time the vehicle is started. It will go through its 3 stage routine, initially delivering a high voltage to force current into the battery, then eventually going to float mode. The problem arises from the system of switching between the three modes of operation. Most dc-dc chargers include a delay, some only a few minutes but others may take hours to change from serious charging to float mode. During this time excess current may be forced into a fully charged battery, even though all its reagents have already been used up. This causes damage.

How to avoid this? Either turn off the dc-dc charger (or set it manually to float mode) when the battery isn't being used, or maybe deliberately use the battery as per the original poster's query, so the charger can do its job properly. In other circumstances I would simply leave the battery fully charged when not in use.

Hope that makes sense!

Cheers

John





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Follow Up By: Rimbus - Sunday, Feb 17, 2013 at 21:12

Sunday, Feb 17, 2013 at 21:12
Thanks John
Would it therefore be fair to say that by not having a multi stage or DC/DC charger, ther risk of overcharging is removed?
Cheers
Dave
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Follow Up By: Rimbus - Sunday, Feb 17, 2013 at 21:13

Sunday, Feb 17, 2013 at 21:13
I should add that asuming the vehicle alternator functions as it should.
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Follow Up By: Member - John and Val - Monday, Feb 18, 2013 at 08:53

Monday, Feb 18, 2013 at 08:53
Hi Dave,

The overcharging issue really only arises when a dc-dc charger is involved, and only then because the charger goes through its whole routine every time the engine is started, regardless of battery state of charge.

Like the dc-dc charger, the alternator initially delivers a higher charging voltage (typically about 14.4V) to suit the cranking battery and return it quickly to fully charged after starting the engine. The alternator output usually drops after a few minutes, so (in the absence of a dc-dc charger) while the auxilliary battery may see the higher alternator voltage, it won't be for long and shouldn't worry the aux battery.

To directly answer your question - By not having a dc-dc charger the risk of overcharging the aux battery is very slight and may be ignored. I run a dc-dc charger (excellent!) and my practice is to leave it turned off when the aux battery isn't being used, but every few weeks turn it on for a few minutes to replace any charge lost to leakage.

Cheers

John



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Follow Up By: Rimbus - Monday, Feb 18, 2013 at 18:08

Monday, Feb 18, 2013 at 18:08
Brilliant, Thanks John.

I have a 1994 model, so there is only one bit of fancy electronics in it, the radio.
This is my 3rd 4wd, but 1st time I have a AGM battery, so I am making sure I have things set up correctly.
Cheers
Dave

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Follow Up By: Allan B (Member, SunCoast) - Monday, Feb 18, 2013 at 23:20

Monday, Feb 18, 2013 at 23:20
John,

I did consider the overcharge potential (lol) when responding to Rimbus but decided to ignore it as he was charging from an alternator which would probably cause little overcharge. However in my own case with two AGM aux batteries, each with its own Redarc BCDC1220 I thought it could be an issue and I did give some consideration to it following the installation.

In actuality, upon starting and with fully charged auxiliaries, the individual ammeters show 5-10 amp for about 30 seconds then drop to 0.5A for about 90 seconds then to zero current indefinitely. In truth there is probably some small float current below the induction ammeter's resolution. So I concluded that there was no significant overcharge.

Redarc's description of their algorithm seems to bear out my observations. It would seem that the algorithm for these chargers upon detecting a "fully-charged" battery causes a quick transit through the Boost and Absorption stages and into Float without undue overcharge. That is not to say the case is the same for all brands and models of DC-DC chargers so your warning is still valid.

My identical batteries are situated with one in the engine bay and the other in the cabin. The battery in the engine bay is a few months older and it draws a little more initial charging current than the other which may indicate some self-discharge due to both age and the exposure to engine bay temperatures, but there is not much difference.


Cheers
Allan

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Follow Up By: Rimbus - Tuesday, Feb 19, 2013 at 07:06

Tuesday, Feb 19, 2013 at 07:06
I'm like the vehicles you bloke appear to be driving.
1994 Troopy HZJ75, turbo for me.

Allan, I guess it is a case of buying the good gear with the Dc/Dc charger, no problems will come out of it. Pay peanuts......get monkeys etc.
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Follow Up By: Member - John and Val - Tuesday, Feb 19, 2013 at 08:07

Tuesday, Feb 19, 2013 at 08:07
Hi Allan,

I'm always mindful when responding to matters here that there is a big silent audience watching the discussion. It's easy to lead folks astray by omitting some fact that may not be directly relevant to the original question but is important to the rounded out the discussion.

The possibility of overcharging deserved a mention as some dc-dc chargers take a long time to drop back into float mode. One I've heard of takes literally hours! Mine takes about 20 minutes, so I leave it turned off when the batteries aren't being used. (When the batteries are being used on a trip, running the fridge and all the other gear, charging torches, phones, cameras, running the radios....etc... it is excellent.) Sounds like yours responds more quickly to a fully charged battery.

Dave - It isn't really a matter of pay more to get better - rather different manufacturers use different ways of detecting the state of a battery. There's a degree of averaging involved and it sounds to me that Allan's charger averages voltage and current readings over a shorter time than mine does. Both valid, both quality items, just different.

Cheers

John

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Follow Up By: Member - bungarra (WA) - Tuesday, Feb 19, 2013 at 09:19

Tuesday, Feb 19, 2013 at 09:19
Hi Allen/John & Val

Interesting comments re the dc-dc charger. I have just installed a CTek D250S in my vehicle. Would you care to comment on its management style at start up on a fully charged aux battery please?

In other words is it more along the lines of Allens or maybe I should consider putting in an isolator such as John & Val have

Thanks

Graeme
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Feb 19, 2013 at 11:20

Tuesday, Feb 19, 2013 at 11:20
Hi John,

You are quite right about dealing with overcharge even if it was not directly related. It was remiss of me to ignore it.

It is fortunate that the Redarc BCDC's behave as they do because I had not considered overcharging when initially installing them. Another feature of the Redarc's is that they will not drain the cranking battery attempting to charge the auxiliary in the event of an alternator failure, as happened to you near the end of your 2011 trek. In discussion with a Redarc engineer I learned that their chargers briefly disconnect the load every 20? seconds (to eliminate line-drop) and verify that the input is above 13 point something volts. This ensures that the input is coming from an alternator and not just from a charged cranking battery yet still allows the charger to operate down to a specified 9 volts to allow for line-drop. Crafty eh?

I do not know if any other DC-DC chargers do this. Yours obviously does not. What brand is it?

Cheers
Allan

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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Feb 19, 2013 at 11:59

Tuesday, Feb 19, 2013 at 11:59
It occurs to me that the Redarc system referred to above may have a problem with some of the new vehicle systems where the alternator output is controlled to a sometimes low voltage by the EMS.
Maybe Redarc will address this. Alternatively some after-market 'chipping' may modify the alternator algorithm?

Cheers
Allan

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Follow Up By: Member - John and Val - Tuesday, Feb 19, 2013 at 11:59

Tuesday, Feb 19, 2013 at 11:59
Graeme,

The D250S combines the switching, dc-dc charging from the alternator plus an MPPT solar charger all in one unit, which is great. I have no experience with it, so can't comment on its charging algorithm. I have heard that early versions of it took quite some time to decide that a battery was fully charged - not good if the battery is already fully charged when the alternator starts up.


What do I use? A 30A dc-dc charger shown here. I carry two 100 Ah batteries connected in parallel mounted close together in the back of the Troopy, and the 30A charger is excellent. (A bit too big for a single 100Ah battery.) Although my charger includes provision for a remote ON/OFF switch, for historical reasons I use a heavy duty relay under the bonnet to disconnect it (and other stuff) when not required. I don't think the D250S has provision for turning on and off internally - pity, as you'd have to deal with both the alternator input and the solar input if doing it manually.


Like Allan, I have meters monitoring aux battery voltage and current, and clearly visible when travelling. Well worth the small cost to know just what's going on.


Cheers

John

Cheers

John
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