Normal battery to run fridge

[Woolly]

Hi All, hoping for advice from someone who understands electrical stuff better than me. My D1 is set up for a dual battery system, but currently (!) lacks the second battery, which ideally should be deep cycle. I hope to go on a four day trip in the near future, driving every day, but cannot foresee any other excursions, and there is a good starting battery in my Rangie. Would it be feasible to use the Rangie's battery as the second one, mainly just to run the fridge?
Thanks, Woolly.

[drivesafe]

Hi Woolly, and depending on both how much driving you do each day and how power hungry your fridge is, you may get away with just using your existing cranking battery.

But for safety sake, having a second battery is by far the best way to go.

It is up to you as to what you think will be best!

You say you have a dual battery setup, what type of dual battery isolator is it?

If it is a DC/DC type then any battery will do.

If it is a solenoid type isolator then a CRANKING battery is a far better choice.

Deep cycle batteries are all good and well but are slow to recharge, so if you have a DC/DC setup, because DC/DC devices charge slowly, a deep cycle battery is fine.

But if it is a solenoid type isolator, as your alternator can put out a lot more amps than any DC/DC device can, using a CRANING battery as the auxiliary battery is a much smarter setup, because cranking batteries, particular newer ones, are specifically designed for FAST recharging.

So even a short drive will see much more energy replaced than any DC/DC setup could hope to do.

Also note, most people are unaware that cranking batteries, when used as an auxiliary battery, can be used very successfully for deep cycle applications, but dedicated deep cycle batteries SHOULD NOT be used to start vehicle motors.

[AK83]

Hi All, hoping for advice from someone who understands electrical stuff better than me. My D1 is set up for a dual battery system, but currently (!) lacks the second battery, which ideally should be deep cycle. I hope to go on a four day trip in the near future, driving every day, but cannot foresee any other excursions, and there is a good starting battery in my Rangie. Would it be feasible to use the Rangie's battery as the second one, mainly just to run the fridge?
Thanks, Woolly.

Do you already have a solenoid for connecting/disconnecting the second battery from the main starting one in the D1?
That is, you say the D1 is set up for dual, and this implies that you already have a VSR type unit installed.
Or have you made room to fit a battery?

No problem to use the Rangies' battery to run the fridge for a short while. Is it a modern fridge with a low volt cutoff feature, that is when the battery gets to 10.something volts the fridge turns off. You don't want a battery draining too much, as it will permanently damage it over time.

You also need a way to cut off the starting battery from the second battery if voltages get low too, otherwise start battery will drain too.

[drivesafe]

Is it a modern fridge with a low volt cutoff feature, that is when the battery gets to 10.something volts the fridge turns off. You don't want a battery draining too much, as it will permanently damage it over time.
It is actually NOT a problem to discharge a battery to a low state, PROVIDING, you can recharge it.

The problem with continually discharging a battery to a low state, is when you do not recharge them, leaving them constantly in a low state.

All cranking batteries, when used as an auxiliary battery, can be safely discharged down to 20% SoC and many of the newer cranking batteries can be safely and regularly discharged to 0%.

Again, this is OK as long as you can recharge them to a reasonably high state of charge between uses.

[Woolly]

Thanks for the prompt replies and info. You have probably saved me a couple of hundred dollars. Just to clarify, the battery controller is a TJM VSX unit, about 20 years old, and the fridge a Waeco CF 50, about 10 years old and running fine, and they have a low voltage cut out. Thankfully, D1's (and RRC's) were built with second battery trays which is great. The trip I am doing will involve several hours driving each day, so there should be no worries about charging (I hope). If I have to buy another battery in the future, an All-Rounder type may be the way to go so it can be used in either situation.
Thanks again, Woolly.

[drivesafe]

If you decide to go with a second battery, have a look at SuperStart Batteries HVT range.

All-Rounders are good batteries, but the HVT batteries can be safely discharged down to 0% SoC ( All-Rounders recommend no lower than 20% SoC), so you get 20% more usable capacity for the same size battery.

Also, All-Rounders are a Calcium type battery while the HVT batteries are AGMs, meaning the HVTs are easier and quicker to fully charge.

[shack]

I have NOT got on well with SSB batteries, HVT or otherwise. YMMV of course but I've been pretty disappointed.

[AK83]

I have NOT got on well with SSB batteries, HVT or otherwise. YMMV of course but I've been pretty disappointed.

Yeah, me too.

Started well in my Tdi for about 6 months, and slowly got worse. After 3 years, let me down completely, when after a 45min drive it didn't have any juice to start the Tdi, and the secondary batterys' power just got drained into the SSB instead of give it a helping hand.

[drivesafe]

I have NOT got on well with SSB batteries, HVT or otherwise. YMMV of course but I've been pretty disappointed.
Hi shack and I have had a few customer say the same.

But hundreds of others have done well with them.

The thing is that the HVTs being AGMs, do not require special charging to get them to a fully charged state.

Whereas, All-Rounders, which are a pretty good battery, but being a calcium/calcium battery, they do need a periodical high voltage charge to keep them in a fully charged state.

This is something MOST alternators just can not do.

[350RRC]

The question also involves how good the insulation of the fridge is.

I bought a 40l Primus about 15 years ago, same price as an Engel at the time but the insulation on the Primus is nearly twice as thick. Came with the usual sort of cover.

Used it last September for a week in the back of a Courier 4WD tray ute, set at 1 degree C and shut off at 10.5 V.

This car only has a small car type battery (72 Ah, 380CCA), but I did take a 1500 amp Noco heart starter just in case.

The remote readout for the fridge in the ciggie lighter showed it operating the whole time at 1 to 1.5 degrees and the voltage never got below about 11.5 overnight from memory.

Ute started unaided no probs every morning.

DL

[Slunnie]

The question also involves how good the insulation of the fridge is.

I bought a 40l Primus about 15 years ago, same price as an Engel at the time but the insulation on the Primus is nearly twice as thick. Came with the usual sort of cover.

Same thinking. I bought an Evakool esky and was just so impressed that I bought the ED50 fridge/freezer (no longer available) which is the same esky but turned into a fridge. If your fridge is good like that, then just turn it off at night, it will probably stay cold, your battery will hopefully be fine and then just turn it on again when you start driving the next day.

[Woolly]

Thanks again for all the replies and extra info. Once more, AULRO has resolved my concerns and I have learned more about batteries and my vehicle along the way.
Cheers, Woolly.

[MLD]

Whereas, All-Rounders, which are a pretty good battery, but being a calcium/calcium battery, they do need a periodical high voltage charge to keep them in a fully charged state.

This is something MOST alternators just can not do.

Hi Tim, what voltage output is "periodical high voltage"? My puma religiously sat on 14.2-14.4V output. The LS engine going into the Puma is a newer style PWM controlled alternator that is regulated by the BCM based on whatever parameters defined by factory. However in my situation, being an engine conversion, i am running a module that permits me to set the duty cycle of the alternator, with max potential of 15.5V. Adjusting the duty cycle is not something i can do on the fly, so looking to preset the duty cycle output that is a balanced compromise that suits most situations.

[drivesafe]

Hi MLD, if you have a Calcium/Calcium battery, it would need a 15.5v charge, once a month, otherwise 14.4v or thereabouts would be fine for the rest of the time.

If you have an AGM battery, NEVER run higher than 14.7v at anytime.

The early model D4s actually had a good Cal/Cal charging setup, but you had to have it changed if you swapped out the Cal/Cal cranking battery for an AGM cranking battery.

Today everything is much simpler because just about every vehicle comes with an AGM cranking battery.

[PhilipA]

I would at least have a lithium starter pack with me, (I do) in case you leave a light on as well or something.
Seeing it is most probably an auto, it is darned hard to start them with a flat battery. A D2 TD5 will not start under about 11.5 volts .
Regards PhilipA

[Captain_Rightfoot]

It's hard when you haven't tried things out. The answer "it depends".

Early fridges like the engel were small and very efficient because they had to be. People these days don't seem to worry about that and run big power hungry fridges and have big electrical systems.

My 40l Engel uses 2-3 Amps an hour. If I run the starlink which I would like to do (I mean you could switch it on and off as required) it's 2a an hour. Say you pull up at 4pm and drive out at 9am. .. that's 17 hours at 5a an hour. If you take 85A from a standard cranking battery there is not going to be any starting from it in the morning without help. :o

Things you could do is pick a small efficient fridge, and keep charging to while the car is running. Pick led lights and maybe handheld. Be conscious that you're going to have to drive every day or charge somehow or the fridge is going to flame out. Maybe you know someone who has a solar panel you could borrow?

Also be aware that even if a battery says it has 110 amps (say) it's not really very good for it to use more than half of it. Up until recently I had a Drivesafe SC80 (??) that linked the two batteries together (cranking and agm) down to a point. I used this for 20 years with my engel fridge. If moving every day no problems. If doing two days was a bit grim.

I've just replaced with a lithium battery and DCDC charger. $$$$$$....

[drivesafe]

Also be aware that even if a battery says it has 110 amps (say) it's not really very good for it to use more than half of it.
Hi Captain and sorry mate but this is pure advertising fiction, put out by companies trying to convince you that you get more power out of a 100Ah lithium battery than you can get out of a 100Ah lead acid battery, ( AGM or Wet Cell )

There is no such limitation of only using 50% of a lead acid battery and most lead acid battery manufacturers specifically state that their lead acid batteries, when used as auxiliary batteries, can be SAFELY discharged down to 20% SoC and many of the newer AGMs, like the SSB HVT range of batteries, can be safely discharged down to 0%.

Yet most lithium batteries are internally limited to only be discharged down to 20% and some are limited to just 25%.

So you are actually more likely to get more usable energy from a lead acid battery than you are for a lithium battery of the same Ah.

[Captain_Rightfoot]

Hi Captain and sorry mate but this is pure advertising fiction, put out by companies trying to convince you that you get more power out of a 100Ah lithium battery than you can get out of a 100Ah lead acid battery, ( AGM or Wet Cell )

There is no such limitation of only using 50% of a lead acid battery and most lead acid battery manufacturers specifically state that their lead acid batteries, when used as auxiliary batteries, can be SAFELY discharged down to 20% SoC and many of the newer AGMs, like the SSB HVT range of batteries, can be safely discharged down to 0%.

Yet most lithium batteries are internally limited to only be discharged down to 20% and some are limited to just 25%.

So you are actually more likely to get more usable energy from a lead acid battery than you are for a lithium battery of the same Ah.
Thanks! That's really interesting.

Victron say this for AGM. It does suggest big discharges are hard on them - but 400 cycles is a lot. My batteries die from age I suspect rather than use. The lithium battery I bought state 6000+ cycles at 80% DOD. Time literally will tell if they are as good as they say.


Rated capacity: 20 hr. discharge at 25?CFloat design life: 7-10 years at 20?C
Cycle design life:
400 cycles at 80% discharge
600 cycles at 50% discharge
1500 cycles at 30% discharge

https://www.victronenergy.com/upload/documents/Datasheet-GEL-and-AGM-Batteries-EN.pdf

[drivesafe]

Hi again Captain and the use of cycle rates, in my opinion, is nothing more than a scare tactic.

BUT you made a VERY IMPORTANT observation when you state that "your batteries die from age rather than from use"

Most people do not realise this as being the usual cause of the demise of a battery.

Cycle rates are really irrelevant and I'll give you an example of why I state this.

If you have a battery with a 200 cycle to 0% SoC life expectancy, then if you went camping EVERY weekend and EVERY weekend you discharged the battery down to 0% SoC, you will only get 4 years of use from than battery.

If you only went camping once a month, then you should get 16 years of use. NOT GOING TO HAPPEN.

I no longer make any reference to cycle rates when discussing battery life expectancy, whether it be for lead acid batteries or lithium batteries, for the above reason.

[Captain_Rightfoot]

Hi again Captain and the use of cycle rates, in my opinion, is nothing more than a scare tactic.

BUT you made a VERY IMPORTANT observation when you state that "your batteries die from age rather than from use"

Most people do not realise this as being the usual cause of the demise of a battery.

Cycle rates are really irrelevant and I'll give you an example of why I state this.

If you have a battery with a 200 cycle to 0% SoC life expectancy, then if you went camping EVERY weekend and EVERY weekend you discharged the battery down to 0% SoC, you will only get 4 years of use from than battery.

If you only went camping once a month, then you should get 16 years of use. NOT GOING TO HAPPEN.

I no longer make any reference to cycle rates when discussing battery life expectancy, whether it be for lead acid batteries or lithium batteries, for the above reason.
Very considered Tim. Thank you.

I'm fortunate the batteries in my defender live a very sheltered life in the box under the seat. I just replaced my batteries from 2018 (both cranking and AGM). Not because they weren't working, just because I felt I should. But they only get a couple of hard weeks a year.