Wiring solar panel on car

Submitted: Monday, Oct 26, 2020 at 18:27
ThreadID: 140678 Views:1566 Replies:16 FollowUps:26
I have a guy who will install a solar panel on my car (with a regulator). He will wire the panel to the starter battery, so that will always have full charge, then the aux. battery will get charged through isolator. Does this seem like a good idea or should the panel be wired to the aux. battery?
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Reply By: Member - Rod N (QLD) - Monday, Oct 26, 2020 at 20:09

Monday, Oct 26, 2020 at 20:09
Wire to the aux, that is where to loads should be. The starter battery should not have a requirement to be charged by solar. In fact the aux should be charged by the alternator through the VSR.

Have a look at the Cetek 250. This should satisfy your needs.
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Reply By: Tlax - Monday, Oct 26, 2020 at 20:49

Monday, Oct 26, 2020 at 20:49
Rod, I did ask the guy why he wouldn't connect to the aux and it was 'just in case - better to ensure the starter has full charge'. And the aux will still get charged. Seemed logical to me, but I am not experienced in 12V setups.
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Follow Up By: Gbc.. - Tuesday, Oct 27, 2020 at 06:43

Tuesday, Oct 27, 2020 at 06:43
The Ctek mentioned above and others will do the isolating you need, and will direct the solar panel power to the second battery until it is charged, then will also charge the start battery as you wish. It is the orthodox method of doing things.
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Reply By: Athol W1 - Monday, Oct 26, 2020 at 21:43

Monday, Oct 26, 2020 at 21:43
Tlax
Whilst either method of wiring will achieve the results it is more usual for the solar charger to be wired to charge the auxiliary battery, and should you be using a DC to DC charging method then it will charge the auxiliary battery.

Should your car be fitted with a 'smart' alternator, or if you are using a Lithium battery for the auxiliary, then you will need a DC to DC charging system to make the system operate to the maximum potential.

Hope this helps.
Athol
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Reply By: HKB Electronics - Monday, Oct 26, 2020 at 22:56

Monday, Oct 26, 2020 at 22:56
Just to complicate it even further, if you really want to charge the main some VSR's are dual sense, ie solar panel connected to aux will also charge the starter battery.
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Follow Up By: baznpud - Tuesday, Oct 27, 2020 at 15:58

Tuesday, Oct 27, 2020 at 15:58
Yep, agree with above remark, that's how we have ours wired in.
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Reply By: Tlax - Tuesday, Oct 27, 2020 at 07:25

Tuesday, Oct 27, 2020 at 07:25
Would there be any issue charging the starter battery by the alternator and solar panel at the same time?
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Follow Up By: qldcamper - Tuesday, Oct 27, 2020 at 11:28

Tuesday, Oct 27, 2020 at 11:28
None at all.
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Reply By: Phil G - Tuesday, Oct 27, 2020 at 08:20

Tuesday, Oct 27, 2020 at 08:20
If you have a DC-DC charger separating the batteries then connect a small charger (such as the solar panel) to the cranking battery, the DC-DC will suck the cranking battery dry because the small charge triggers the DC-DC charger to continue working.
Try it some time!
This guy alterted me to it - he demonstrated it with a Redarc. I've made it happen with a Projecta and an Enerdrive.
https://youtu.be/rDXixCzg6iw

In any case, should always connect to aux battery because the charge current that continues to top up the cranking battery at a couple of amps is not going to the aux that needs it.
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Follow Up By: Athol W1 - Tuesday, Oct 27, 2020 at 10:54

Tuesday, Oct 27, 2020 at 10:54
Phil G.

That is NOT my experience.

I have a Dmax that is fitted with the 'smart' alternator, I also have a Lithium auxiliary battery that is charged via a Redarc BCDC1225D and also a solar panel, and is supplying a compressor fridge that is never switched off.

On several occasions since March this year the vehicle has been 'parked up' in the garage, and as the fridge depleted the aux battery I used a Ctec GS4000 to maintain the starter battery. In this configuration the Ctec was continuously charging the start battery whilst ever the auxiliary battery required a charge. The Ctec charger does NOT have a setting for Lithium batteries.

The Redarc (which is set for Lithium battery charging) operated as a pulse charger to the aux battery, the pulses being for the length of time it took the starter battery to go from the Redarcs programmed switch on voltage (approx 13.2v) to its programmed switch off voltage (approx 12.6v), then waited until the starter battery again reached the system switch on voltage before repeating the process. When the aux battery was fully charged, and the start battery likewise, then the Ctec went into float mode.

All that the blue wire does is tell the Redarc system that there is a 'smart' alternator fitted and this changes (lowers) the 'switch off' voltage when the vehicle ignition switch is in the on position (to approx 12.1v). It DOES NOT cause the system to completely discharge the start battery.

The operating voltage of the Isuzu Smart Alternators varies between 12.2 and 16 volts, depending on state of battery charge, park lights on and throttle position, and there may be other parameters that Isuzu are not telling us about.

My only connection to Redarc is as a user of their products.

Regards
Athol
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Follow Up By: Phil G - Tuesday, Oct 27, 2020 at 13:07

Tuesday, Oct 27, 2020 at 13:07
Hi Athol,

If you hook up a charger until all batteries are charged then you will not know there was a problem
unless you measured and recorded how many amps were going into the DC-DC charger early on in the charging process.

A flat cranking battery can occur if you disconnect the charger well before charging is complete. Nothing to do with your Dmax, or what type alternator you have or whether you've connected the blue wire that changes the voltage settings. All to do with the fact that most DC-DC chargers can be fooled into still operating when there is a small charge continuing into the cranking battery.

The question being asked by the original poster is whether solar panels should be connected to the cranking battery. If he has a simple isolator, there would be no problem. But if he has a DC-DC charger, then there is.
While the solar panels are charging the cranking battery the DC-DC charger will be triggered to work and most will draw additional current from the cranking battery and drain the cranking battery. Once the panels are removed or the sun goes down, the cranking battery might be depleted enough to prevent the vehicle from starting.

I'm not making this up. It is a very easy thing to demonstrate with an ammeter. On my vehicle I hooked up a 7A Ctek charger to the cranking battery and once the DC-DC charger was triggered to work I measured a full 30A of charge current going to my Lithium auxillary batteries. I also noted my cranking battery voltage dropped as well.
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Follow Up By: Athol W1 - Tuesday, Oct 27, 2020 at 14:23

Tuesday, Oct 27, 2020 at 14:23
Phil G.

I hear what you are saying, but that was not my experience.

At the time I had volt and amp meters in the system, and every time that the starting battery voltage dropped then the DC to DC charger 'cut out' and protected the starting battery. One of the functions of any decent DC to DC charger is to act as a VSR, and that is exactly what I found to be happening.

When the start battery voltage was sufficient then the charge rate to the Aux battery did go to the maximum for the charger (25amps, would have been greater should I have measured it at the starting battery), and when the start battery voltage dropped to approx 12.5 volts then the charge amps went to zero. At no time did I see a start battery voltage below 12.4v.

The voltage measured across a battery when the charger is on and when the charger is off will only vary by a very small figure, unless the battery has an internal open circuit issue. NOTE, this does NOT apply when using Lithium batteries as the primary battery, or if the charger is connected directly to a Lithium battery.

Regards
Athol
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 14:41

Tuesday, Oct 27, 2020 at 14:41
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Phil and Athol,

I think you will find that both behaviours can exist and that it all depends on the starter battery impedance and the threshold settings of the dc-dc charger.

The starter battery impedance, and that includes the resistance of the connections, will affect the difference between the true inner voltage of the battery compared to the voltage appearing at the post terminations which is what the dc-dc charger perceives. A battery with higher impedance (aged) will exhibit larger terminal voltage change per current change.

So you may both be right.

Don't believe too much from Andrew St Pierre White. He is very expressive but not very expert in electrical science.
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Allan

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Follow Up By: Tlax - Tuesday, Oct 27, 2020 at 14:45

Tuesday, Oct 27, 2020 at 14:45
I have a simple isolator, not DC-DC charger.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 15:10

Tuesday, Oct 27, 2020 at 15:10
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Yes Tlax, but is it a voltage sensing isolator or a simple solenoid controlled from the ignition circuit?
Both are employed and both will serve the purpose but can behave a little differently.

The voltage sensing type will behave in a similar manner to a dc-dc charger whereas the simple solenoid is at the absolute control of the ignition key.

If of the second type, then no current could flow from the solar panel to the auxiliary battery when the ignition was off.
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Follow Up By: Tlax - Tuesday, Oct 27, 2020 at 16:28

Tuesday, Oct 27, 2020 at 16:28
Allan, thanks for the info. I have just checked and it is a solenoid battery isolator.
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Follow Up By: qldcamper - Tuesday, Oct 27, 2020 at 16:37

Tuesday, Oct 27, 2020 at 16:37
One would hope the guy you have fitting the system would have already assesed what type of isolator you have before he suggested doing it that way.
Would also hope that the start and house batteries are of the same chemistry and the reg suits otherwise that could cause problems too.
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Follow Up By: Tlax - Tuesday, Oct 27, 2020 at 17:08

Tuesday, Oct 27, 2020 at 17:08
Perhaps he assumed I have a voltage sensing isolator? I do know he has considered which regulator to use, ensuring it is suitable for the max voltage output of the panel.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 17:24

Tuesday, Oct 27, 2020 at 17:24
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Tlax, it is important to determine which type of solenoid isolator you have.

If it is a voltage sensing type then it will be similar to the photo below. It will have a little box attached containing the 'smarts'.

If it is an ignition controlled isolator it will not have a box attached but will have a thin wire attached leading off to an ignition source.

If you are going to connect the solar panel to the starter battery then you must have an isolator with the 'smarts'. With an ignition-controlled isolator, the aux battery will only be connected to a charging source (solar or alternator) when the ignition is on which is not utilising your solar to best effect.

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Follow Up By: Tlax - Tuesday, Oct 27, 2020 at 18:33

Tuesday, Oct 27, 2020 at 18:33
Thanks. This is my isolator:
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 18:53

Tuesday, Oct 27, 2020 at 18:53
.
Yep, that is an "intelligent" or voltage-sensing isolator.
it is rated at 100A max. current, cut in at 13.2v and cut out at 12.7v
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Reply By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 10:23

Tuesday, Oct 27, 2020 at 10:23
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Tlax,

Cars are designed to have the alternator look after charging the starter battery and, properly maintained, it will do that job well. There should be no need to provide the starter battery with additional charge from a solar panel provided that you do not have 'auxiliary' loads connected to it, and you should not do that.

If you do not connect the solar panel directly to the auxiliary battery (via a controller of course) then the auxiliary battery will only receive its charge from the alternator when the engine is running. The solar panel connected to the starter battery will only be directing its efforts to the starter battery which will probably already be fully charged from the alternator as the car maker designed.

There are cute ways to configure these charging circuits but the conventional way I have described above is all that is really required for a reliable system. Just leave your starter battery and alternator as originally built, provide an isolator (or dc-dc charger) to the auxiliary battery and connect the solar panel via regulator to the auxiliary battery. If you have not already purchased the isolator and solar 'regulator' then there are dc-dc chargers with provision for solar input which carry out all functions in the one device.

Cheers
Allan

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Reply By: CSeaJay - Tuesday, Oct 27, 2020 at 10:23

Tuesday, Oct 27, 2020 at 10:23
It is easy to over complicate matters, and many answers is to get it form "pretty good" to "pretty damn good"
Theoretically if your starter is healthy then the charge will simply go through to the Aux. I can see the logic of your installer's thinking. And, at the end of the day, will not make that much difference.
Personally I would (have) connect it straight to the Aux. but no big deal IMO
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 10:41

Tuesday, Oct 27, 2020 at 10:41
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CSeaJay, if using a voltage sensing isolator it will not close until the voltage at the starter battery terminals rise to (typically) 13.5 volts. So the auxiliary battery, possibly in need of charge, is deprived of any until the solar panel is able to raise the starter battery to 13.5 volts. Not an ideal arrangement in my view.
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Follow Up By: CSeaJay - Wednesday, Oct 28, 2020 at 16:00

Wednesday, Oct 28, 2020 at 16:00
Allan

Yes what you are saying makes sense, which is why I said that it will work if the starter is healthy. If the voltage sensing isolator is open, it will only take a couple of minutes to close and let the charge through.
This is why I said I see the logic of the installers thinking.
I have mine wired up to the Aux as I want all power to go to the 1 battery not both. When I am camped and the isolator is closed (connected) I flick my headlights on for 5 seconds which is enough to open it and then 100% of the solar charge go to the Aux and the advantage is that it tops it up nicely.
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Reply By: Pepper - Tuesday, Oct 27, 2020 at 10:36

Tuesday, Oct 27, 2020 at 10:36
As a simple and cost effective alternative ,in my vehicle with solar and dual batteries i replaced the original controller on the solar panel with a powertech mp 3700 dual battery solar controller.

This allows the power from the solar panel to connect to the powertech controller which has TWO power outlets,you connect one outlet to the starter battery (bypassing the voltage sensitive relay or similar ) and the second outlet to the second battery .

The ratio of charge supplied to each battery is adjustable . EG 10% to starter and 90% to second battery or other ratio as required.

In the above example above, 10% and 90% when either one of the batteries reaches full charge 100 %, all of solar charge goes to the other battery ( overriding the preset ratios as needed ) and both batteries are fully charged..

No need for a dc dc charger in many vehicles..

Cost well less than $100.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 10:50

Tuesday, Oct 27, 2020 at 10:50
.
Perhaps I should point out Pepper that the system you describe is only a PWM controller, not MPPT.
And that you still need to have either a solenoid or dc-dc charger to enable auxiliary charging from the alternator.
Cheers
Allan

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Reply By: Pepper - Tuesday, Oct 27, 2020 at 11:01

Tuesday, Oct 27, 2020 at 11:01
Allan in the second paragraph of my post i spoke of the vsr or similar ,i did not suggest to remove it but instead to simply run a wire from the controller to the starter battery to top it up when ignition is switched off , sometimes difficult to describe things in text alone.
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Reply By: qldcamper - Tuesday, Oct 27, 2020 at 12:01

Tuesday, Oct 27, 2020 at 12:01
There have been many times I have seen the start battery discharged accidentally, glove box left open for a couple of days or accessories turned on to power up sockets to charge phones and heater fan left on low speed, many things can do it.

Have a back up plan, set of jumper leads are a forgotten piece of gear these days, only the old fellas carry them these days.

Set up one panel that can be connected to the start battery if required.

My back up is a 6 inch shifter and screw driver, if the start battery fails I will just swap it out with one of my accessory batteries (AGM)

As Allan hinted towards, leave the original system alone and keep your accessory system as simple as possible, just have a back up plan for your particular set up sorted.
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Oct 27, 2020 at 12:18

Tuesday, Oct 27, 2020 at 12:18
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I agree qldcamper.

I have mine setup so that nothing is operable from the starter battery when the key is off. Even the headlights require ignition on to operate. Otherwise it is too easy to run the start battery flat when camped.

For emergency starting, I can jump start from the auxiliary batteries in the back, and being an "old fella" I do have a pair of very heavy jumper leads. I can weld with them! Mind you, I confidently expect to only use them to start 'other peoples' cars. lol
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Reply By: Phil G - Tuesday, Oct 27, 2020 at 13:24

Tuesday, Oct 27, 2020 at 13:24
If you use an isolator for your second battery then you'll just be wasting solar power.
If you have a DC-DC charger, then it can actually flatten the cranking battery.

This video explains it well:

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Follow Up By: CSeaJay - Wednesday, Oct 28, 2020 at 16:05

Wednesday, Oct 28, 2020 at 16:05
Very good to know!
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Follow Up By: Stephen L (Clare) SA - Wednesday, Oct 28, 2020 at 20:35

Wednesday, Oct 28, 2020 at 20:35
That’s very interesting Phil, thanks for sharing
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Reply By: axle - Wednesday, Oct 28, 2020 at 08:51

Wednesday, Oct 28, 2020 at 08:51
So where's RMD to sort this out!?.....LOL.


Cheers.
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Oct 28, 2020 at 09:02

Wednesday, Oct 28, 2020 at 09:02
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Oh Axle, it's sorted. Let sleeping dogs lie. lol
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Allan

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Reply By: qldcamper - Wednesday, Oct 28, 2020 at 10:45

Wednesday, Oct 28, 2020 at 10:45
Tlax,
Sorry if you have mentioned these details before but what type are your batteries and what is the size of the solar panel you are intending to fit?
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Reply By: Member - Cuppa - Wednesday, Oct 28, 2020 at 14:06

Wednesday, Oct 28, 2020 at 14:06
There is an issue which I don't think anyone else has yet mentioned. It is something which has arisen in a friend's Patrol recently & relates to battery types & usage.

In his case he had a maintenance free wet crank battery, & a wet auxillary battery able to be topped up. Problem was he rarely thought to top it up, & this combined with the fact that his aux battery was only ever used when away on camping trips meant that it remained at 100% charged, or close to it much of the time when the car was being used as a daily driver at home. When wet batteries are charged to 100% they bubble & gas, unlike crank batteries which are in regular use & rarely get charged above 70% to 80%.

The 'problem is that VSR 'reads' the crank battery voltage to determine when it connects/disconnects the two batteries to/from each other, so the situation arises that the aux battery is full or close to it, but each time the ignition is turned on the voltage in the crank battery rises in response to the input from the alternator, & the VSR joins up the two batteries , allowing the aux to receive charge.

This is not a problem when on camping trips because the aux has constant loads on it.
However in the 'daily driver' scenario the aux gets overcharged. Combine this with not keeping the wet aux regularly topped up & it is a recipe for premature battery death, most likely evidenced, as in my friend's case by a bulging swollen battery & green oxidation around the battery caused by it's excessive venting.

Some things will help to avoid this. Use of a Valve Regulated Lead Acid battery (VRLA) like an AGM (Absorbed Glass Mat) type which are less prone to venting (but need to be better shielded from heat, when under the bonnet) or a very regular routine of topping up the battery (& not over filling it). Also using the battery during daily driving (eg. switch the fridge on).
Alternatively incorporate a switch/relay so the two batteries only get paralleled when you choose, but you have to remember otherwise you can end up with an aux battery killed prematurely by under charging. A voltmeter in the cab off the aux provides a handy reminder of when to flick the switch.

If the solar panel with regulator is mounted on the car & attached to the aux, the switch allowing the VSR to do it's thing would probably never need switching on in daily driving - but useful on camping trips.
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Oct 28, 2020 at 15:30

Wednesday, Oct 28, 2020 at 15:30
.
Cuppa, you're right about all of that. But I think the best way of dealing with it is to turf the solenoid isolator and install a dc-dc charger to supply the aux battery, no matter what type it is. The cost of the charger can be much less than replacing a battery and it has a better charging profile than the alternator regulator.
Cheers
Allan

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Follow Up By: Member - Cuppa - Wednesday, Oct 28, 2020 at 16:07

Wednesday, Oct 28, 2020 at 16:07
Yes I agree Allan, but not everyone has the cash flow to buy a dc to dc charger, & I tried to add something without making it a VSR vs dc to dc debate. Personally after several years use I would not go back to a VSR, with or without solar input.

I also prefer not to have aux batteries in the engine compartment which makes use of a dc to dc charger easier, as many don't take kindly to being under the bonnet.

For those who are new to the topic - a dc to dc charger is a 'smart charger' which both provides the function of crank battery protection that a VSR does, but is also as it's names implies a charger, not just a switch (like the VSR). Importantly it's a 'smart ' charger, which has a method of determing when the aux battery is full, & will then drop it into 'float' mode, to maintain it;'s charge, but not overcharge it. If the aux is a wet battery, it will still require topping up now & then, but probably not as frequently. In conjunction with not over discharging the battery it will ensure a much longer battery life. So yes, in the longer run it is both a cheaper & better option.

Just in case someone reads this & decides to put the aux battery inside their vehicle - DON'T DO IT if it is a wet battery! AGM is OK for this though.
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Reply By: Tlax - Wednesday, Oct 28, 2020 at 19:30

Wednesday, Oct 28, 2020 at 19:30
To follow up a couple of messages, I will likely have the fridge running all the time, and I have attached a pic if the starter and aux batteries.
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Follow Up By: qldcamper - Wednesday, Oct 28, 2020 at 20:22

Wednesday, Oct 28, 2020 at 20:22
Both a similar type of battery, servicable so be sure to check the electrolite level every service.
What type of vehicle is it?
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Follow Up By: Tlax - Wednesday, Oct 28, 2020 at 20:55

Wednesday, Oct 28, 2020 at 20:55
2010 Ford Ranger PK
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