Dual battery set ups - have I misused my own battery?

hockayak

New Member
Hi all,

A while back (November 2017) i fitted my own dual battery set up. It wasn't too tricky, having followed a bunch of advice on here. I'm 100% certain that its wired well, appropriate diameters for the cable runs etc. I bought the Thunder DC-DC charger (cheapish) off ebay, and a 115Ah AGM battery (Again cheapish off ebay). Initially it the set up would charge and power our Waeco CFX 50W for three days or more, with the fridge set to cut out use at its middle battery level setting. Now several years on the output/usage is totally woeful, as in a matter of hours, even though its "fully charged" i.e. I could drive for 24 hours straight kind of charged. The battery has lived in my rig, connected to the charger/alternator since bought, obviously I haven't run the fridge the whole time, day trips, camping trips etc.

Now i have some questions:
1) How long would a battery like this be expected to last?
1a) How can i tell if its totally dead?
2) Is the Thunder DC-DC charger reasonably well respected? - Does it treat batteries well/charge them appropriately?
3) Should a dual battery be disconnected if it isn't going to be used for a while?
4) Does constant mini-top up charge and lack of use kill the battery?

We are happy to buy a new battery/charger, but clearly would love some advice, link to information to avoid doing the same again.
 

CTL

Well-Known Member
Four and a half years for an AGM is pretty good. What is the voltage at the battery terminals after it has “fully charged”?
 

Hoyks

Well-Known Member
Batteries die over time.
The happiest lead acid batteries are ones that are kept at a moderate temperature, don't get discharged much and are kept fully charged in between uses. Last week we had to change the batteries in a fire truck, 17 years old, always on a trickle charger or with the motor running when out of the shed. 3 days parked up without the charger or motor running, the isolator left on and the fridge plugged in killed effectively them.

1. I expect around 5 years from a battery, for the past few cars I'd run a dual battery system until the 2nd battery died, move the starter down one and buy a new starter battery. Just battery isolators, and batteries under the bonnet, no cleaver chargers, but they averaged out around 5 years each. I wouldn't be horribly upset with 4 years either.

1a. Fully charge it, disconnect it from all load and leave it sit for a few hours. Anything under 11V and its probably stuffed. Some will still put out 12.4V, but have no capacity to cope with a actual load though. A battery shop can load test it and tell you if that's what you've got.

2. No idea. A DCDC is only as good as the power supply though, they should keep a battery charged fully, but if the power supply to the charger is inadequate they can't work to their full rated capacity.

3 & 4. See my 1st comment, a happy battery doesn't get drawn down much and is constantly topped up (but not over charged). Taking them out, they sit in the shed, get forgotten and slowly discharge.
 

Triton14

Well-Known Member
Hi all,

A while back (November 2017) i fitted my own dual battery set up. It wasn't too tricky, having followed a bunch of advice on here. I'm 100% certain that its wired well, appropriate diameters for the cable runs etc. I bought the Thunder DC-DC charger (cheapish) off ebay, and a 115Ah AGM battery (Again cheapish off ebay). Initially it the set up would charge and power our Waeco CFX 50W for three days or more, with the fridge set to cut out use at its middle battery level setting. Now several years on the output/usage is totally woeful, as in a matter of hours, even though its "fully charged" i.e. I could drive for 24 hours straight kind of charged. The battery has lived in my rig, connected to the charger/alternator since bought, obviously I haven't run the fridge the whole time, day trips, camping trips etc.

Now i have some questions:
1) How long would a battery like this be expected to last?
1a) How can i tell if its totally dead?
2) Is the Thunder DC-DC charger reasonably well respected? - Does it treat batteries well/charge them appropriately?
3) Should a dual battery be disconnected if it isn't going to be used for a while?
4) Does constant mini-top up charge and lack of use kill the battery?

We are happy to buy a new battery/charger, but clearly would love some advice, link to information to avoid doing the same again.

Batteries don't last forever but how you treat them will prolong their life.

1stly things I have come to learn is not all batteries are equal & what they maker can state/claim as capacity is not really able to be verified as true until you can test it out.
One of the best indicators of capacity is its overall weight(AGM'S anyway).
I posted on here a while ago that an ebay 170Ah battery weighed the same as a 110Ah of a reliable make!



Don't draw the battery past 50% of its charge, which us 12.05v, every time this happens you lose longevity.

Disconnect the battery if not in use & yes keep it trickle charged or check its state of charge to make sure it's not under 12.05v.

Use the search tab on here, you will get more info.
 

Les PK Ranger

4x4 Earth Contributer
A good hit with a desulphating charger occasionally will also help keep things in good order.
SCA have reasonable ones like these for a decent price . . .

2 x 6 amps models . . . all you really need . . .
https://www.supercheapauto.com.au/p...-battery-charger/587423.html?cgid=SCA01060203

Or a 10 amp if you want a little quicker charging . . .

I used to charge mine overnight about once a month, both starter (wet) and 2nd battery (AGM).

Besides heat, vibrations kill batteries, so try and mount with some sort of shock absorption.
I had a 100 amp/hr AGM in the Ranger, in a battery box (Arkpak) and it went for 4 years before it died.
Bought a new 105 amp/hr and this time I lined the battery box with ~ 10mm med density foam under and around the battery.
It was still going strong when the vehicle was written off, some 6 years later.
That was a SSB (Super Start Batteries) off 4WD Extreme ebay, still just $322 delivered.
 
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Triton14

Well-Known Member
A good hit with a desulphating charger occasionally will also help keep things in good order.
SCA have reasonable ones like these for a decent price . . .
Very true, I have used this function on my Ctek MXS 5.0 & it has rejuvenated the battery & given me another year or so out of it.

I agree that you do at times need to put batteries on a 24V charger to get them

Of course @hockayak you need to have a multi meter to check the battery is holding charge as they may have dropped a cell.
 

Bru9

Active Member
You will be doing yourself a huge favor if you just take the time to learn how batteries and electricity work.

1a you apply a C/20 load or in the ballpark, to your fully charged batt and observe the decaying voltage, if it drops to around 12 4V under load at say 5-10mins you can be sure its stuffed. Most batteries are dead at EOL 80%.
2. No. You never skimp on battery chargers as they are your lifeline. A good solenoid setup is better than a cheap dc-dc.
If its absorb V is close to 14.4, and it has a good absorb timer then should be right.
AGM's must be fully charged after each and every cycle with the correct voltages for the correct time to get long life, but most here put 10cycles on them each year and deal with sulfation with a top up from 240V overnight. So they get decent life. But put 30cycles or more on each year and then you will see the battery degrade quite fast.
3. disconnect from what?
In storage an AGM should be kept on float voltage of roughly 13.8V. If it sits in a rig running fridges each day, this will put wear on it even if solar is always present to top back up.remember lead batteries want to sit on 13.8V overnight to finish the charge...

4. If by top up you mean weekly or daily Yes. Because you are micro cycling and never giving the battery a chance to truley absorb to 100%.
Lack of use does have a negative impact on AGM if it sits for months in storage no floating as it can slowly sulphate, if it sits on float charge much of its life it can also degrade, AGM like to be exercised, I do this by running powerful drain plug on them taking them up and down quite hard every say 4-6months, 8months longest. Haha so much for maintenance free!

And please dont waste your time on the snake oil that is rejuvenators or desulphanators. Is pure BS! No reputable AGM maker would advise one. You buy a quality battery, you look after it, and IF it needs some "de-sulphation" your only hope is equalization "holding the absorb voltage in a precise protocol" toys for suckers...
 

cam04

Well-Known Member
[QUOTE="hockayak, post: 674576, member: 75740"
Now i have some questions:
1) How long would a battery like this be expected to last? The answer is directly proportional to how much you paid - there is no such thing as a cheap battery. You bought an eBay special and 4 years later it is dead. Lifespan is about spot on for what you paid.
1a) How can i tell if its totally dead? Hot beer - or of you have followed your voltages the battery will stop accepting charge at lower voltage.
2) Is the Thunder DC-DC charger reasonably well respected? - Does it treat batteries well/charge them appropriately? More or less
3) Should a dual battery be disconnected if it isn't going to be used for a while? No, as Bru9 said it should float at 13.8v odd whenever you can. My trailer is plugged in constantly
4) Does constant mini-top up charge and lack of use kill the battery? Sort of but that is what we buy them for. It is the deep discharge and partial recharges while out camping that do the real damage. Every minute an AGM is not at 13.8v is shortening its life.

[/QUOTE]
 

Toyasaurus

Well-Known Member
Cam is quite correct about getting what you paid for.

I had 2 optima yellow tops in the back of my rangie, hooked up to a 150amp relay that was switched on when I remembered.

I treated those things like crap. 17yrs I had them in the truck, and they are still there as far as I know.
 

cam04

Well-Known Member
I’m an optima fan also. Just finished putting the 2013 d31T out of the old Ute into the new one. Not a thought of replacing it yet.
 
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