deep cycle/dual purpose battery?

Hi there.
I have started looking at purchasing a dep cycle batery as a second battery to run my accesories. I have noticed some batteries described as deep cycle but also dual prpose with high CCA for starting.
I thought deep cycle was very differen to cranking batteries, so am a questioning these batteries. Any comments?
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Reply By: Battery Value Pty Ltd - Wednesday, Apr 28, 2010 at 21:34

Wednesday, Apr 28, 2010 at 21:34

starter batteries are designed to deliver enough amps down to minus 18 degrees.
Because any battery will drop off in capacity as well as internal resistance at lower temperatures, they're made with a high active surface area in an attempt to offer enough leeway to the negative temperature affects.
In other words, they have a higher number of relatively thin plates (electrodes) and just as many gaps between them filled with electrolyte.
Deep cycle batteries are the opposite. Because the plates are thicker, and their number is smaller, there are less spaces. You could say deep cycle batteries have a higher lead 'fill factor'. That's why they're heavier than starter batteries.
And because lead is the most expensive ingredient in a lead acid battery, they're also dearer.
Because cranking only requires about 250A max, a sizeable deep cycle battery offers low enough internal resistance to supply this kind of current - under normal temperatures. But at -18 degrees, the same battery will struggle while the starter battery with the high plate count will just keep cranking (if it's fully charged).
So in Australia deep cycle batteries can be used for cranking most of the time.
One reason why this isn't really recommended is because of the higher than ambient under-bonnet-temperatures, and you can't afford to lose electrolyte in a sealed lead acid battery.
And the other reason is, that if you draw a lot of Ah before starting, your typical deep cycle battery will take tens of hours to get fully recharged with the low 13.8V alternator voltage.
So you want a good charging system for any deep cycle battery on bord (or recharge it regularly by a good mains charger).
The charging system needs to output 14.7V of boost voltage for quick recharging. But even then, it may still take longer than 10 hours to fully charge a 80% discharged deep cycle battery.
Starter batteries never get discharged more than to 90% SOC normally, so this is a non issue because they're operated in float mode basically. If you tried to discharge a starter battery more than this on a regular basis, the recharging times will increase dramatically, and at the same time the battery will suffer from effects like positive grid corrosion (which raises the internal resistance and leads to grid embrittlement). Because you then will operate your starter battery in a partial state of charge for most of the time, the battery will also sulfate up.

If you want excellent cranking and good deep cycle properties combined in one battery you'll have to look at a variation of AGM: pure lead/tin, spiral wound.
There is one for you to check out:

For any questions, just use the form on the page, or post back here.

Best regards, Peter
AnswerID: 414631

Follow Up By: Sand Man (SA) - Wednesday, Apr 28, 2010 at 22:49

Wednesday, Apr 28, 2010 at 22:49

Well written reply mate.

Just one comment I would make. I once had an Exide Orbital version of the spiral wound battery you mention.
Good performer and not too heavy but as they are only rated at around 50 Ah, they don't provide a lot of capacity either.



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FollowupID: 684811

Follow Up By: Battery Value Pty Ltd - Thursday, Apr 29, 2010 at 00:02

Thursday, Apr 29, 2010 at 00:02
thanks Sand Man,

yes true, spiral wound offer less capacity per Dollar.
That's because of the care and effort which goes into making them.

But they have outstanding properties including the highest vibration and shock resistance, the least gassing potential and therefore better suited to warm operating environments, high active surface area to weight ratio, the lowest internal resistance, pure lead tin chemistry with less side reactions thus less corrosion and positive electrode weakening, increased charging current acceptance and current limit. And last but not least, they are the best performers under partial state of charge conditions, meaning they keep the internal resistance low even if significantly discharged (high Peukert number). So if your starter battery carks it, you can rely on your spiral wound AGM to deliver the cranking amps even if it's low on charge.

Needless to say that you can easily fix the issue of limited capacity by doubling up, but there is no way you can add these nice features to other designs.

Best, Peter
FollowupID: 684814

Reply By: Peter_n_Margaret - Wednesday, Apr 28, 2010 at 21:55

Wednesday, Apr 28, 2010 at 21:55
I am using a Fullriver HGL120 (120Ahr AGM) quite successfully as a crank battery in the OKA. It is NOT "under the bonnet", so excessive heat is not an issue. I use Fullriver DC115s for the house.

OKA196 Motorhome
AnswerID: 414632

Follow Up By: Battery Value Pty Ltd - Wednesday, Apr 28, 2010 at 22:48

Wednesday, Apr 28, 2010 at 22:48
Hello Peter,

interesting setup! I'm curious about the alternator voltage(s) in your OKA - or is there an additional source for charging like solar?

Best regards, Peter
FollowupID: 684810

Follow Up By: Peter_n_Margaret - Thursday, Apr 29, 2010 at 21:22

Thursday, Apr 29, 2010 at 21:22
Yes Peter.
There is 600W of solar, 460Ahrs of house DC115s and a 2 way 200A Redarc link to the crank (which I can mostly leave open). The alternator is 14.3V at the crank battery and the 8M of cable to the house is 70mm2.
If the house is low (12.1V), the 85A alternator will send 70A to the house for a while and provide a rapid bulk charge that the solar can top up and finish off.
When closed, the RedArc effectively adds the "top" of the HGL crank to the house system (down to 12.3V?) and the solar tops up the lot when the sun shines.

We run a 1300W PSW inverter for power tools, bread maker, electric blanket...
We have no shore power plug-in capability, no 240V charger and no generator.
Would like a fuel cell though and would be tempted to dump a house battery to ballance the weight.
More here...OKA196 Motorhome

OKA196 Motorhome.
FollowupID: 684947

Reply By: Member - Phil G (SA) - Wednesday, Apr 28, 2010 at 22:20

Wednesday, Apr 28, 2010 at 22:20
The real life difference between deep cycle and cranking batteries is not much. A lot of what you read is hype. One battery retailer admitted to me that their deep cycle batteries were the same as their cranking batteries with a different sticker and half the warranty.
AnswerID: 414634

Follow Up By: Maîneÿ . . .- Wednesday, Apr 28, 2010 at 23:24

Wednesday, Apr 28, 2010 at 23:24
Maybe they're a shonky organization and we should be informed or warned ?

Peters well written reply above clearly states a major difference that can be readily ascertained is the battery weight, you will then understand a bit more about *quality* Deep Cycle batteries v Cranking batteries when you understand the reasoning.

Usually only 'low weight' batteries are rated as both high CCA and high RC, as heavy weight DC batteries are not rated as Cranking batteries simply for the reasons Peter has stated.

Then there are Hybrid, Marine batteries and AGM batteries to consider also.

Maîneÿ . . .
FollowupID: 684812

Follow Up By: Member -Signman - Thursday, Apr 29, 2010 at 10:26

Thursday, Apr 29, 2010 at 10:26
Hiya Phil,
Maybe you could supply me the details of your 'battery retailer'- I could send him a cutaway of a standard cranking battery and a deep-cycle battery.
The difference is obvious- even to a mug like me !!

Maybe 'their' batterys are the same with different labels (and prices I guess)- but I would call that rip-off!!!!

FollowupID: 684845

Follow Up By: Member - Phil G (SA) - Thursday, Apr 29, 2010 at 14:27

Thursday, Apr 29, 2010 at 14:27
I should have prefaced my first sentence by saying "wet cell" deep cycle and saying it was about 10 years ago - before AGMs became common. To the consumer, they usually look identical, and in the past, it was common practice for the retailers to have a pallet of batteries and to put the stickers on themselves. They were not any of the usual brand batteries. Hopefully its not as common any more.

Back to the original question, I like many of my 4wding friends have used cranking batteries as our auxillary batteries for 25 years. Like any battery, they last if you look after them - protect them from the heat, keep them charged and don't discharge them past 50%. That's easy to achieve if you go driving every day and live in a cool climate. I usually change them as a pair every 4 years. Exide Extreme and the Century Overlander have been the pick of the bunch for me.
FollowupID: 684878

Follow Up By: Spade Newsom - Thursday, Apr 29, 2010 at 20:34

Thursday, Apr 29, 2010 at 20:34
Phil, at how many volts do you consider a 12v battery 50% discharged.
FollowupID: 684940

Follow Up By: Member - Phil G (SA) - Thursday, Apr 29, 2010 at 22:07

Thursday, Apr 29, 2010 at 22:07
FollowupID: 684955

Follow Up By: Anton123 - Saturday, May 08, 2010 at 13:24

Saturday, May 08, 2010 at 13:24
Hi all

Thanks for the batteries update. I would appreciate some advice on replacement options.

I have a Sep/06 HDJ100 with what looks like factory fitted dual batteries. (80D26R's... I am assuming the D is for deep-cell). I purchased the vehicle second- hand and am also assuming that these batteries are the originals.

As the weather is getting cooler but not freezing (inland of mid north coast - NSW) I am having early morning starting issues and the passenger side battery appears to be out of charge, one cell in particular is hissing loudly after stopping and this battery is very hot even a few hours after the vehicle has stopped.

The driver side battery appears to be OK charge wise, however, does not appear to be able to start the vehicle by itself. I have isolated this battery and trickle charged overnight. The volt meter in the vehicle moves to just under 13.8 when ignition is turned on and the vehicle is moving.

My question.

Should I replace this passenger-side battery with another deep cycle and keep the drivers side as is, or are there any other suggestions. What type of battery(ies) should I consider?


FollowupID: 685913

Follow Up By: Maîneÿ . . .- Saturday, May 08, 2010 at 13:33

Saturday, May 08, 2010 at 13:33
I would replace *both* batteries with Cranking batteries
batteries recommended for Cranking purposes

Maîneÿ . . .
FollowupID: 685917

Follow Up By: Member - Phil G (SA) - Saturday, May 08, 2010 at 17:52

Saturday, May 08, 2010 at 17:52
Your problem is because your bubbling battery has shorted a cell (so it has 5 cells instead of 6). The 5 cells are taking full alternator voltage, so are being overcharged, making them hot and and giving off gas. Problem is that the bad battery will pull current out of the good battery, so you end up with two flat batteries. So you will need to replace both batteries. Also, your current batteries are cranking, not deep cycle.

Naturally there are a couple of choices here. The simplest is to buy two normal wet cell cranking batteries. I would buy the bigger N70 size (12" long) because they fit nicely in the cradles and will give you a bit more capacity. My favourites have been the Century Overlander or Exide Extreme batteries. There are a heap of others out there - my only advice is to stay away from Calcium batteries - they never get fully charged by Landcruiser alternators - the voltage is not high enough for many calcium batteries.

Many 100series owners split their batteries - they put the bigger N70 batteries in and fit an isolator between the two. The passenger side battery becomes the sole cranking battery and the drivers side becomes the auxillary. Your vehicle will start fine on one good cranking battery.
FollowupID: 685939

Reply By: ChipPunk - Sunday, May 09, 2010 at 15:57

Sunday, May 09, 2010 at 15:57
Good to see some informed battery knowledge!
Also a recognition of the different construction methods.

Some statements are not incorrect but somewhat interesting - like AGMs gassing less that wet cells. (I usually describe it as not overcharging (over-volting) an AGM because they cannot dissipate gas etc and instead may initiate a thermal runaway, and (hence) also the danger of AGMs with collapsed cells.)

A cranking battery sold as a deep cycle would have a lesser warranty because either can be used as the other - they just won't last as long.

Where dual-battery set-ups have been sought - although it depends on the aim & application - I usually recommend a simple co-charging arrangement with the standard battery and whatever other battery is desired - eg, AGM if not vented; deep-cycle for fridges and drive-in theater audio systems ; crankers for audio SPL competitions and doof ride-through.
I strongly advise against parallel batteries when merely idling (not being charged, not with a reasonable load) even if they are "matched".
In most systems, the difference between a permanent parallel battery installation and one that is paralleled only whilst charging is a mere relay - typically $10 for 60A etc.

Where wet-cells can be used, I was recently impressed by a $180 dual-terminal deep-cycle wet-cell with ~760CCA & 100AH .

And despite the old 70/30 rule - where you shouldn't discharge deep-cyclers/crankers more than 70%/30% - being surpassed by alleged 90% and even 100% dischargeable deep-cycles, the word still seems to be "not more than 50%".

The only other thing I seem to consistently hear is how over-rated certain big name AGM/VRLA batteries are. O for the life of me, I won't mention their nameO. (But both have cheaper rebranded versions.)

Finally - as I just wrote in another thread - despite deep-cycles not being good for cranking, if their capacity is big enough, the cranking current has a lesser impact. (Is it too late to mention a "parallel during cranking" bypass where only deep-cycle batteries are used?)
AnswerID: 415987

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