Dual Battery Help

[Brass]

Hey guys,

Disclaimer: The Patrol was bought used a month or so ago, and I am still new to this stuff, so I am not 100% on these things. So apologies if I get anything wrong here.

Currently setting up my Patrol for a big lap, and my main concern right now is getting the electrical work right. The current setup has a redarc isolator, and the aux battery looks to be this one, and it is housed in the engine bay.

I've checked the voltage on the aux battery a few times since we got it, and it looks to settle around 12.55 volts or so. My most recent measurement was after the truck has been parked for over a day, so should be no residual charge. I have also driven the truck a few medium-ish city drives (30-50 km each way) over the last couple of weeks, and have not seen the batteries voltage go up at all (after settling). I've followed the 1 cable going out from it, and it looks to only be hooked up to the UHF radio, which is basically always off, so nothing should be draining it. When I fire up the engine, the alternator looks to be working just fine, as I get a reading of 14.35V. I've tried looking up the specific voltage chart for that battery, but so far have not found anything.

For the 6-8 month trip we have planned, the only meaningful power draw will be coming from our 75L Engel combi fridge/freezer. I have some cheap 200W solar panels to charge it on days we will not be driving, but would think we would be on the road every 2nd day for the bulk of the trip.

So my question is: Should I stick with this battery?

From the research I have been able to do on it, it is not a true deep cycle, which worries me a bit. That being said, as long as it can power the Engel for 24 hours straight without dropping below the safe recharging threshold, I think I can survive (though 2 whole days without any recharge would be a nice cushion). But on the flip side, I want to keep costs to a minimum. Every $200 is an extra week we can extend the trip by. So while I would love to redo the whole thing with a DC to DC charger and 2 AGM batteries in the back, I would rather have the extra month on the road.

So, if my suspicions are correct and the battery is not charging fully/properly (and if anyone has a recommendation on how I can better test that I'm all ears), then I could use some advice on what to replace it with. I've read that AGM batteries should not be stored in the engine bay, as they do not handle heat well. So if I go that route, should I get some 6 gauge wire, run it from the starter to the rear of the truck, and stick the AGM there (currently have a ton of 8 guage twin core, but that is probably too thin a wire I think?)? Should I replace the battery with a new wet battery of some kind? And either way, should I look to replace the isolator with some kind of DC to DC charger setup?

Thanks for reading this. I'm open to any and all feedback on this, and happy to provide any info that might help make things clearer.

[Yeti's Beast]

The set sounds ok and that voltage is normal for the battery. Even if you put a charger on it, it wil increase in voltage slightly for a while.
Remember and this will sound weird. Your alternator is not a battery charger. It’s a battery maintainer.
If your unsure of your batteries health. Take it into a Battery World store and pay them to run an Astratec discharge test to see what it’s capacity is.
It’s like simulating running something off the battery over a period of time.
It draws a 20 amp load and times how long it gets to a pre set voltage. They compare the time with a chart to determine its capacity.
This will take at least a day to do.
Best results come from a dc-dc and an agm or lithium away from heat but the old Redarc VSR and a deep cycle battery have been used for years without problem.
Remember the KISS theory.
keep It simple stupid.


Sent from my iPhone using Tapatalk Pro

[Shephead]

Your setup and planned driving every couple of days with 200w solar in between sounds ample to me. Similar to my set up.
And just like mine, sounds like your battery needs replaced. They are a consumable remember so don’t be surprised if they need replacing every 2-3 years.
Your Engel has a low voltage cut out yes? Set it to 12v. I used to set mine lower, but realise the error of my ways now!

[Shephead]

Meant to say- do your own load test. Run fridge for 24 hours with no charging/driving. If voltage drops down towards 12v then your battery is likely sulfated- it may say it’s full and won’t take more charge but it’s capacity has been reduced loads. That’s what mine is doing right now.

[10G]

Here's another way to think about this.

If you're not going to be away from civilisation, it's not as critical. If you are going to be away from civilisation then it matters more.

If you're sticking around near towns & the battery dies, then you should be able to pick up a new battery anywhere and if you can undo a few nuts and bolts you should be able to remove the old and insert the new without any dramas.

However, if you're going to be away from civilisation for some time & the battery dies, then you'll be in a bit of a pickle. In this case, you may like to replace it before you leave.

I reckon that's how I'd handle this issue.

[Cuppa]

Here's another way to think about this.

If you're not going to be away from civilisation, it's not as critical. If you are going to be away from civilisation then it matters more.

This advice from 10G is excellent.

I think your battery is probably ok, but it would be wise to do as suggested & take to a battery place to have them do a discharge test. You then know what you are dealing with & can make an informed decision as to whether to replace it or not.

Battery replacement in much of Australia will cost you more than it would at home, so if you have *any* concern about the health of your battery bear that in mind. The specs of that battery suggest that the terminals are opposite those of the common N70 batteries. If that is so expect extra 'hassle'/cost' if cables need to be extended to fit whatever available battery you can get in remote areas.

If funds are tight going with what you have will probably get you by, but will restrict your ability to stay that extra day or two in those special places if you have cloudy (poor solar) weather.

With your current set up your battery will never get to more than around 80% full - this roughly equates to the 12.55v you have seen on your wet battery. Theoretically your setup could fully charge it but the reality is that you cannot drive sufficient hours in a day to do so.

If you were able to charge the battery to 100% this gives you 20% 'extra' capacity, quite significant. Your fridge freezer, depending upon temperature settings & ambient temperatures & a couple of other factors, will probably require between 40Ah & 60Ah per 24 hours. If you have your 105Ah battery 100% charged this will take it down to a 40%-50% State of Charge (SoC), which is *just* sustainable. Add in lights, radio, water pump etc etc you would be pushing it, add cloudy weather & you could be in trouble. What is sustainable for a weekend away is quite different to what is sustainable for longer periods without regular visits to caravan parks to plug in (& then you need to have a decent mains charger).

With your current set up the max charged capacity of your battery will never be more than around 80-85 Ah at best. Pull 60Ah (or more) out of that then that is taking the battery regularly down to around 20% SoC which is a recipe for premature battery failure. You might get 12 to 18 months if lucky. That might be ok if prepared to buy another battery when needed, but as your battery is not brand new you might get a lot less.

If it were me, I would probably want a battery with a higher capacity - 120Ah minimum, bigger if space allowed, & I would want to be able to fully charge it. To do this requires a smart charger.

All solar chargers are smart chargers (some are much better than others, but that's another story), or a dc to dc charger.
To be able to fully charge whatever battery you decide upon, your current one or a replacement, you essentially have 2 choices.

1. Plan to drive long enough each day to let your aux battery charge to 80% & stop early enough to to get the solar panel out for long enough to let it 'top up' the battery to 100% (Goes into float mode).

2. Install a high amp dc to dc charger which will charge your battery to 100% whilst you drive, arriving at camp with a fully charged battery.

It is true that if charging as you currently do the battery may charge up to 80% a bit quicker (if heavily discharged) than with say a 40amp dc to dc charger, but the latter will continue to take the battery to full.

The best option is a DC to Dc Charger plus the solar. Arrive at camp, put out the solar panel which would be enough (in most circumstances) to keep the battery at 100% until nightfall, meaning your battery would only need to see you through until next day's sunrise &/or next day's driving. Going this way clearly gives you a lot more flexibility as to your 'going or stopping' decisions. From my perspective this is well worth added cost of a DC to DC charger.
This one gives you a better Solar charger (than the crap stuck onto the back of many panels) & a 40A dc to dc charger for around $400 to $450 in a single unit https://enerdrive.com.au/product/epo...rger-40a-plus/


By charging the battery regularly to 100% will also make your battery last longer before needing replacement (This is the main reason why properly charged deep cycle batteries have more than double the lifespan of 'starter' batteries.

Currently your system is charging the aux battery as though it were a starter battery - so a 4 year lifespan would be a reasonable average.

A disadvantage of 'wet' batteries compared to AGM/Gel batteries is that when being fully charged they will bubble & gas. This means that they need regular checking & topping up with distilled water. Easy enough to do, but just as easy to forget. AGM's don't have that problem (& also have the advantage of charging more quickly & having a much slower self discharge rate if left unused for periods of time). For this reason my preference is for an AGM Aux battery - they also stand up to corrugations better). There are a number of AGM batteries which seem to survive just fine in under bonnet temperatures.

Hope this helps.

[10G]

Another thing I'll throw in here is the bang for buck thing, this realisation helped me just before I was about to spend big bucks on lithium.

Q: What's difference between a $200 battery that lasts 2 years and a $1000 battery that lasts 10 years?
A: Nothing, they both cost $100 a year.

I know lithium has several benefits over a typical AGM etc, but if none of those advantages are needed or wanted then .....

[threedogs]

Ive had the RedArc dual battery thingy now coming up on 10yrs its a fit and forget option .
I do have a CTex dc 2 dc charger Iv yet to fit have all the bits just need a body ha ha

[Shephead]

If your getting 14.35v across aux battery terminals from alternator, then it should charge to 12.8V. Probably 13.2 or something, then dropping to 12.8 over a few hours. If it doesn’t, I’d say the problem is your battery. Save yourself the hassle and spend $200 on a new one. :-)

[Brass]

Thanks for all the advice guys, really appreciated.

I think my plan for now is:
I have a sparky mate willing to help out this weekend, and we will run the 8 gauge wire to the rear of the vehicle (and set up all the anderson plugs, fuses, etc). This will give me a chance to test the battery with the Engel fridge for 12-24 hours. If it holds its charge roughly as expected, then great. I'll probably go to battery world after this as well to see about that health check just to confirm. If it does not hold charge, then its an obvious replace.

Either way, Cuppa and Yetti's Beast make great points that it is probably not enough should a literal rainy day occur (and I do not want to leave yet). And while 50-75% of the trip will be at least somewhat near civilization, a minimum of 25% of it will be completely out in the bush (eg. Plan to do at least 7 days across the Gibb River Road, and would love to just sit in Cape Range national park, or Karijini for a few days without moving)

So this leaves me with 2 options in my mind. Either get a new 120-140AH battery to replace the current one (the obvious choice should the current battery turn out to not hold charge). or I could get a 100-140AH AGM to throw in the back that is completely detached and only charges via solar.

For the first option, does anyone have any recommendations on deep cycle batteries (AGM or wet) that can live in the engine bay half decently. Was busy today, so did not have time to measure what the current tray can hold.

For the second option, I would likely have a setup where I could swap anderson plugs to power the fridge via the front aux batter, then switch to the rear aux battery. Does that seem sane?

I think both these options take Yeti's KISS advice to heart, and involve the least amount of electrical work. It also lets me get some work done this weekend that will not go to waste. As much as I would love a dc to dc charger setup, I cannot find one for less than 250 that looks even halfway decent. And the good ones seem to be at least 500.

Once again, thanks for all the feedback so far. It's been really good, and helped me start to make a better plan going forward.