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

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

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

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.....

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.

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

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.

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

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

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

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.

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

Hi Ribus,

This is a promo video but has some interesting info.

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

Cheers

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.

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