Dual Battery question

I am looking to replace the second battery in my Prado. I have recently upgraded to a 150 series Prado and the N70 size second battery that I had in my previous vehicle doesn't fit. The largest capacity battery I can get in the size that will fit is 80AH which should be fine for my needs. My question is which type of battery should I get?

The main duty will be running my 50 litre Waeco fridge plus a few other accessories but these would normally only be used when driving. Our camping mostly involves touring where we are on the move every day and occasionally we will spend two nights in the one spot.

I have searched this site and others and the more information I get the less easy the choice seems to be.

The choices seem to be standard wet cell deep cycle battery (i.e. maintainable type), maintenance free calcium batteries and AGM batteries. The batteries I am looking at are the Supercharge Amp-Tech deep cycle, the supercharge Allrounder calcium-calcium and a AGM, the name of which I can’t remember. I’m in a small-ish town where the choice of batteries available is limited.

Questions/issues about each battery as as follows:
Amp-Tech – traditional wet cell deep cycle battery so I’m sure will perform well. The worry I have about this battery (and any similar deep cycle) is how robust they are – I will be travelling the Canning in a couple of months and don’t want it to fall apart from corrugations. Is this really and issue or am I worrying about nothing?

Allrounder – more robust than the amp-tech and same amp-hour capacity. But, being a calcium battery I believe it will need a higher charging voltage but the new Prados actually have a lower than usual charging voltage from the alternator – only 13.6-13,8 volts. Therefore I will never get it even close to fully charged while travelling. I have purchased a voltage booster (have not fitted it yet) but don’t know if the extra voltage (claimed extra 0.5-0.6V) will be enough.

AGM – on paper this is the best choice. Fast charging rate, no maintenance and very robust. They cost the most but I am willing to pay more for the right battery. Downside is weight – it will be going under the bonnet and the later model Prados have a reputation for cracking around the second battery tray. The specific one
I am looking at is apparently designed for under bonnet use.

In my previous vehicle I had an N70 size Exide Extreme which met all my needs. But now having to go to a smaller battery means I would have to drop down in capacity in the Exide Extreme which I don’t want to do. the N70 size was 80AH so the next size down would be around 60AH.

So, which way would people recommend I go?

Back Expand Un-Read 0 Moderator

Reply By: Member - Bill B1 (NSW) - Saturday, Apr 16, 2011 at 21:31

Saturday, Apr 16, 2011 at 21:31
Look at your battery tray because the 120 series broke their mountings too with a little bit of dirt road work. It would be worth beefing up the mounting plate on the fender under the tray and strengthen the weld on the bracket that goes off the side. Or any other mounting area.
As for a battery, I think you are restricted to whatever will fit in the biggest capacity available. If you normally maintain your batteries, why not go for a wet cell.

Bill B

My Profile  Send Message

AnswerID: 451457

Reply By: Member - Corrugate75 - Sunday, Apr 17, 2011 at 06:40

Sunday, Apr 17, 2011 at 06:40
All I can offer is I wanted to fit an AGM (Power Sonic brand) under the bonnet of our Patrol and the local advised against it. The reason being: AGMs don't handle heat real well as they can't dissipate it because they're sealed.
I rang the manufacturer (actually the importer) of this AGM and they advised the same, AGM's not real suitable under the bonnet due to engine heat. I mounted the AGM on the camper trailer, and now have a deep cycle under the bonnet.
Other advantage is you can use a deep cycle as a starting battery (if it became necessary) whereas I believe AGM's are not good as a starting battery.
Hope that helps a little.
AnswerID: 451484

Reply By: Member - Bruce C (NSW) - Sunday, Apr 17, 2011 at 07:55

Sunday, Apr 17, 2011 at 07:55
Hi Ando,

On these pages over the last couple of years I have seen posts supporting Corrogates line and several more supporting the use of AGMs under the bonnet without any problems.

One poster suggested that as the batteries are fitted at the front of the vehicle they get more draught and so are kept cooler than the rest of the engine bay. One thing one poster said was that it is advisable to ensure you have the sort of battery cradle which thermally isolates the battery from the engine bay to some extent.

I have read another post where the fellow said that he had an AGM as his start battery, they make them for that job as well, and another for his aux battery and was very happy with his setup and encountered no problems.

I would suggest that if you have a divided battery compartment, partially thermally divided from the rest of the engine bay, then I would take a chance.
AGMs are arguably the best batteries and you don't get the leaking that you inevitably do with flooded cell batteries.

Cheers, Bruce.

At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

Lifetime Member
My Profile  Send Message

AnswerID: 451494

Reply By: Member - Carlin - Sunday, Apr 17, 2011 at 08:51

Sunday, Apr 17, 2011 at 08:51
Thanks for the replies.

I would love to have an AGM but I think the additional cost and the risk of overheating under the bonnet are making me move away from them.

I'm leaning to the Allrounder.

AnswerID: 451501

Reply By: Maya M - Sunday, Apr 17, 2011 at 09:02

Sunday, Apr 17, 2011 at 09:02

I am looking at another battery for our Prado and am leaning toward the Optima yellow top - you have a range from cranking to deep cycle for any application. By their design they are extremely good on corrugations. If your primary fails this will still perform. The size is good for return power.

I am looking at cranking ability - I am running a winch / compressor. You pay a little more but from the reviews I have read it is definitley a sound investment.

Hope this helps.


AnswerID: 451504

Follow Up By: Maya M - Sunday, Apr 17, 2011 at 09:03

Sunday, Apr 17, 2011 at 09:03
Here is the link

FollowupID: 724117

Reply By: Sand Man (SA) - Sunday, Apr 17, 2011 at 09:08

Sunday, Apr 17, 2011 at 09:08
Hi Ando,

May I suggest you do yourself a favor and forget about mounting a second battery in the engine bay. You only introduce problems such as space requirements, heat issues and stress cracking problems down the track.

Because you state your main use will be to run a fridge which will be carried in the back, why not mount your battery right next to it?

With a good quality battery case such as the Sidewinder Flyer and an AGM battery which will not spill its contents, or give off harmful gases, you will have a total solution in one box.
You can also plug in other devices you may use while travelling by means of a suitable patch lead, so there will be no additional cabling issues involved.
The Flyer comes with all installation cables to enable it to be charged from the alternator and includes a built-in isolator to protect the starting battery.
Derek also has an excellent mounting bracket available to secure the battery to.

I have no connection to Sidewinder and am merely a satisfied customer.

Whatever the brand, an AGM battery will give you the best solution for your needs.

Just one other recommendation I will offer.
If your fridge doesn't have a built-in low voltage cut out device, by one as an accessory and install it between your battery and fridge. They are quite cheap and will protect your expensive AGM battery (or any other) from being discharged too low.


I'm diagonally parked in a parallel Universe!

My Profile  My Blog  My Position  Send Message

AnswerID: 451506

Follow Up By: drivesafe - Sunday, Apr 17, 2011 at 10:02

Sunday, Apr 17, 2011 at 10:02
Hi sand man and it’s a bit of a myth that AGMs are any safer than flooded wet cell batteries ( FWC ). Your standard AGM will gas at a lower voltage than a FWC and that means you actually have more chance of cooking an AGM and when they cook, they spew electrolyte so are no safer than FWC batteries

As for gassing, again, AGMs will cook at a lower voltage but if you smell them gassing, they are stuffed. With a FWC, if you smell them gassing, you simply top them up with some distilled water and no harm done.
FollowupID: 724128

Follow Up By: Sand Man (SA) - Sunday, Apr 17, 2011 at 15:20

Sunday, Apr 17, 2011 at 15:20
I can't agree with you.

NOBODY would install a wet cell battery in the back of a vehicle's cab, or in a camper.
Tip them over and they will spill crap everywhere and without venting, mere charging will create explosive gases.

No myth mate.

That is why AGM batteries are safe inside vehicles, as well as marine situations.

Never heard of anyone with problems with an AGM battery in a confined space.

I'm diagonally parked in a parallel Universe!

My Profile  My Blog  My Position  Send Message

FollowupID: 724163

Follow Up By: drivesafe - Sunday, Apr 17, 2011 at 17:16

Sunday, Apr 17, 2011 at 17:16
Hi Sand Man and sorry but again another myth.

There is the reverse mentality that if you use flooded wet cell batteries inside the cab of a car, 4x4 or under the bed or seats of a caravan, that they need to be vented.


The minimum ratio of hydrogen to atmosphere that is needed to make the hydrogen/air mix explosive is 4.1% hydrogen.

The IEEE has set a maximum safe hydrogen to atmosphere ratio of 2% and there is only so much hydrogen a lead acid battery can produce based on the amount of electrolyte in a lead acid battery.

There is a calculation put out by the IEEE that gives the minimum amount atmosphere needed to make it impossible to get a hydrogen to atmosphere ratio of 2% and this is formulated based on the VOLUME amount of electrolyte not exceeding 0.28% of the surrounding atmosphere.

Now as no battery manufacturer lists the volume of the electrolyte in their batteries ( and they don’t need to ) so unless you are prepared to empty a flooded wet cell battery and measure the volume of the electrolyte, you won’t really know the volume of the electrolyte is.

I use a VERY rough way of calculating to determine the minimum atmosphere in a vehicle or caravan or storage shed or what ever needed to be safe for a given battery ( or batteries ).

I measure the total volume area of a battery by measuring the length, width and height ( over the battery housing not over the terminals ) then I measure the volume area of the place the battery is going to be mounted/stored.

I then multi the battery’s volume by 200 and if this figure is less than the volume of the area where I intend to place the battery then, even in a worst case scenario of a total overcharging of the battery, the amount of hydrogen that battery can produce, can not exceed 2% of the surrounding atmosphere.

This calculation has a very large margin of error factored in to make the calculation safe.

This equates to the average 4x4 being able to have 3 x 100 Ah batteries in the cab and even if all 3 were cooked dry, there still would not be enough hydrogen in the cab to cause an explosion.

As long as the area around a battery is open, then ALL batteries, no matter what type they are, are actually much safer than they would be if in a battery box.

This is fact not fiction.

One more point, when mounting a battery inside a vehicle or caravan, say under the bed or seats, while you do not need to vent the battery because there is a sufficient volume of atmosphere, you still need to mount the battery in a secured plastic battery box, even when it’s a sealed battery like an AGM.

Again, all batteries will spew electrolyte if they are over charged for what ever reason, so ALL batteries should be in a plastic battery box when mounted inside a vehicle or van.
FollowupID: 724174

Follow Up By: Member - Phil G (SA) - Sunday, Apr 17, 2011 at 18:26

Sunday, Apr 17, 2011 at 18:26
Gday Bill,
If you want to know Derek's view on a very similar subject, have a read of this thread.
FollowupID: 724181

Follow Up By: Sand Man (SA) - Monday, Apr 18, 2011 at 07:28

Monday, Apr 18, 2011 at 07:28
Hi Phil,

Yep simple sound advice.
Obviously any battery may malfunction if the charging equipment is not up to scratch.
But that situation is very unlikely to happen by recharging from a vehicle alternator.

AGM batteries, IMO are the safest and most practical deep cycle batteries to use inside a vehicle.


I'm diagonally parked in a parallel Universe!

My Profile  My Blog  My Position  Send Message

FollowupID: 724220

Follow Up By: Member - Phil G (SA) - Monday, Apr 18, 2011 at 07:54

Monday, Apr 18, 2011 at 07:54
While AGMs have a great safety record, I wouldn't advise fitting an AGM inside a vehicle because the dodgy handywork of most DIY 4wders (and some workshops) is a worry. For it to be safe, it needs to be bolted down so it doesn't become a missile in a crash and it needs the best possible short circuit protection. A high rate of discharge or a short can cause an AGM to explode.

95% of DIYers don't realise how easy it is to short circuit a battery. Hpw many fit a fuse or fusible link (matched to the capacity of the wiring) at the pos terminal of every battery in their vehicle/trailer? Then how many cover and protect the pos terminal itself? Lots of things can short out on an exposed pos terminal and melt a battery - everything from a wrist watch to camping gear, or the battery moving.

I agree that I am more paranoid than most, but having seen a battery ignite and explode under the bonnet of a vehicle where the pos terminal was accidentally shorted by the bonnet coming down on it, is one thing that makes me more wary.
FollowupID: 724224

Reply By: Member - Phil G (SA) - Sunday, Apr 17, 2011 at 09:09

Sunday, Apr 17, 2011 at 09:09
Gday Ando,
I personally wouldn't touch a Ca-Ca battery (need too high a voltage, hence won't fully charge in a Prado, and I've seen a couple die on corrugated roads). Its great technology but not suited to many of our 4wds.

The better wet cell batteries I've seen have been Exide extremes and Century/Yuasa Overlanders - both come in an N50 size, which like you say will give you about 65Ah and are suited to the heat, and the charging voltage of your Prado. So that would be my first choice.

Second choice would be an Optima D34 - plenty of people had them last many years under the bonnet - My son has one that is now 10 years old and I tested it the other day and t can still start my diesel motor. They have come down a lot in price - batterydiscounters.com.au sell them here in adelaide for $292.

Third choice would be an AGM provided it is mounted behind the headlight and insulated from heat.
AnswerID: 451507

Follow Up By: drivesafe - Sunday, Apr 17, 2011 at 10:04

Sunday, Apr 17, 2011 at 10:04
Hi phil and not sure where you got the info from but Ca/Ca batteries are the best leap in battery technology in decades.

Ca/Ca are far more robust than any standard AGM and last considerably longer than conventional flooded wet cell batteries. Only the Optima would be better and thats at a much higher price, at around twice times the price of an equivalent Ca/Ca battery and this all makes these Ca/Ca batteries ideally suited for RV/4x4 use.

Furthermore, even with the low operating voltage of your Prado, you can fully charge any battery and while Ca/Ca batteries will not be fully charged by an alternator, it doesn’t mean they will never get them over 60 to 70% charged. The reality is that your alternator can charge a Ca/Ca battery upwards of 95 to 97% and this info is available on one of Exides web sites.

Add this to the fact Ca/Ca batteries charge quicker, gas less, self discharge slower and have a longer life span than standard FWC batteries yet cost the same or LESS, why wouldn’t you use them i a 4x4?
FollowupID: 724129

Follow Up By: Member - Phil G (SA) - Sunday, Apr 17, 2011 at 12:05

Sunday, Apr 17, 2011 at 12:05
Gday Drivesafe,
Good to see you're still around!
I tailored my comments to Ando's original question, and he's supplied very detailed and thought out information which is refereshing!

I've assumed his Prado has the usual regulated voltage of 14.3 down to 13.4 with temp regulation; He wants it as a second battery under the bonnet; He's doing the Canning (ie corrugations galore) in a few months.

Regarding Ca-Ca batteries:
(1) The charging algorithm for most Ca/Ca batteries is a long way from that provided by his Prado's alternator, requiring a period of much higher voltage. (Charging Algorithms). My attempts to find detailed technical information on SuperCharge batteries has failed. If you have access to this, please pass it on - it shouldn't be a secret!
(2) Some brands of chargers (eg Redarc reference) have acknowledged the different charging requirements with the introduction of specific calcium algorithms on their chargers.
(3) Personal experience - (a lot of my travel is in deserts with groups of many vehicles). I can remember 5 batteries dying on corrugated roads over the past 7 years - 4 have been calcium (Delcor and Supercharge), and one was an Exide Gel. It could be just coincidence, but it suggests to me that these batteries don't tolerate corrugations and heat as well as an Extreme or Overlander.

As far as being 60/70/97% charged (My name is not Collyn:-)), if it were to be used as a cranking battery, then chances are it would stay fully charged if driven every day for a reasonable distance. But Ando's stated its a second battery being used for a fridge.

If he owned a Discovery, and was charging the batteries off 240V and sticking to the bitumen, my answer would have been different or more likely I wouldn't have commented :-)

FollowupID: 724144

Follow Up By: Member - Carlin - Sunday, Apr 17, 2011 at 12:58

Sunday, Apr 17, 2011 at 12:58
Phil and Drivesafe,

Thanks for the detailed responses.

FollowupID: 724149

Follow Up By: drivesafe - Monday, Apr 18, 2011 at 10:13

Monday, Apr 18, 2011 at 10:13
Hi Phil, and ALL the info you refereed to, and based your reply on, relates to batteries being charged with some sort of battery charger, which are all constant CURRENT charging devices.

None of it is relevant to the Ando’s question, as he was asking about charging while driving, meaning using his alternator which means we are talking about constant VOLTAGE charging ( also known as TAPED charging ) which is totally different in the way a battery is charged.

Furthermore Ca/Ca batteries have now been around long enough and in large enough numbers to show they not only out perform conventional flooded wet cell batteries, both as cranking batteries and as auxiliary/house batteries and they have a number of characteristics that are better than most AGMs.

Plus in Ando’s case, as with a number of other makes, where his alternator runs at a lower operating voltage, whether it’s his cranking battery or his auxiliary/house battery(s), they will still be fully charged and there are plenty of people out there with these lower operating alternator voltages that can prove they are getting fully charged batteries while driving.

Ca/Ca batteries are the battery of the future but they are here now.
FollowupID: 724254

Follow Up By: Member - Phil G (SA) - Monday, Apr 18, 2011 at 18:51

Monday, Apr 18, 2011 at 18:51
Gday Drivesafe,
I'm listening to what you're saying... maybe the Ca/Ca batteries have improved and I'm being a bit harst based on personal experience ...But in all honesty, I'd still be fitting a battery that is designed to take the corrugations. For me that is still a choice between the Extreme, Overlander and Optima because they have the runs on the board.

FollowupID: 724311

Follow Up By: drivesafe - Tuesday, Apr 19, 2011 at 19:48

Tuesday, Apr 19, 2011 at 19:48
Hi Phil and don’t get me wrong, I think Optimas are one of the best batteries available, BUT AT A HUGE PRICE,
FollowupID: 724436

Follow Up By: Member - Carlin - Tuesday, Apr 19, 2011 at 20:43

Tuesday, Apr 19, 2011 at 20:43

As far as I can determine the Exide Extremes only come in N70 size, but you mentioned they come in N50. I would be very interested in one if they do come in this size.

FollowupID: 724444

Follow Up By: Member - Phil G (SA) - Tuesday, Apr 19, 2011 at 21:12

Tuesday, Apr 19, 2011 at 21:12
Here is the list of available Exide batteries - they list a N50EX. Just need to enquire at a dealer I guess.

Looks like Century have dropped the N50 Overlander. Highest capacity you'll get in that size would be the Remco AGM - 80Ah for $319 from Whitworths.

Nothing huge about $292 for an Optima D34 from the place in Adelaide I quoted! But they are only 55Ah...but its very usable.

FollowupID: 724449

Follow Up By: drivesafe - Tuesday, Apr 19, 2011 at 21:30

Tuesday, Apr 19, 2011 at 21:30
Hi Phil but thats $292 for 55 Ah with about a 10 year life span verses $165 for a Ca/Ca 105 Ah with a common 5+ year life span.

Say you would need two Ca/Ca batteries over the ten years and you would two Optima 55 Ah to last ten years to have the same capacity.

Thats $330 for the Ca/Ca verses $584 for the Optimas.

So the Ca/Ca works out about half the cost of the Optima for the same amount of capacity spread over ten years, and the cost of the Ca/Ca batteries are spread out over five years while the Optimas are an up front total cost.

Again, Optima batteries are better but AT A HUGE COST.
FollowupID: 724452

Follow Up By: Member - Phil G (SA) - Tuesday, Apr 19, 2011 at 22:28

Tuesday, Apr 19, 2011 at 22:28
That other link wasn't quite right.This one lists the N50EX.
FollowupID: 724458

Follow Up By: andoland - Thursday, Apr 21, 2011 at 12:18

Thursday, Apr 21, 2011 at 12:18
Thanks for the link Phil. For some reason I could not see the N50 when I was looking.


PS, I wrote the original post under my wifes login, hence the different name here.
FollowupID: 724607

Follow Up By: Member - Kevin S (QLD) - Thursday, Apr 21, 2011 at 16:15

Thursday, Apr 21, 2011 at 16:15
So after all that can I fit an AGM battery in the back of my Jackaroo? There is no space under the bonnet for a third battery. The two there already there are needed for cranking. I thought one of the reasons for an AGM battery was that in could be used in a confined space.

It is important to always maintain a sense of proportion

2019 Mitsubishi Cross

Lifetime Member
My Profile  My Blog  My Position  Send Message

FollowupID: 724634

Follow Up By: drivesafe - Thursday, Apr 21, 2011 at 16:57

Thursday, Apr 21, 2011 at 16:57
Hi Kevin, first off, as it’s going the back of your Jackaroo, it’s not in a confined space.

You can fit any type of battery inside the cab but no matter what type you use, it MUST be housed in a plastic battery box, because ALL batteries, in certain circumstances will spew out electrolyte.

By putting a battery in a plastic battery box and securing the battery so it can not fly around in the event of an accident and you have the safest set up for an auxiliary battery, mounted insde a vehicle’s cab.
FollowupID: 724638

Sponsored Links