Thread: Normal battery to run fridge

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.

Originally Posted by 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.

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.

Originally Posted by AK83

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.

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.

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.

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

Originally Posted by shack

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.

Originally Posted by shack

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.