12v Battery Questions...

Hi Oldbaz,

The batteries sound like they are in OK condition, so would likley be fine to use.

Mounting them in the front boot is also OK, provided the boot is vented (they can discharge hydrogen - lighter than air).

At 65 a/hr each, that will give a total capacity of 130 a/hr. But best not to discharge below 50% if you want maximum battery life, though going down to say 25% is arguably a good compromise between using your battery capacity and battery life. Thus you have somewhere between 65 to ~100 a/hrs available.

Your fridge draws around 10 amps so you will have between 6 to 10 hours before the batteries should be recharged.

It would be best to install a low cutout device, otherwise the fridge will simply keep running down the batteries and that will significantly shorten their life.

I would also recommend a connection to the alternator, that way you should be able to keep the batteries charged while driving and only need to use them while stopped, but not setup thus the fridge not on gas yet.

Cheers

Captain

Within limits, there is no reason why you can't use these batteries in the front boot of your caravan.
The main thing you need to consider though is that wet cell batteries need to be secured to stop any spillage. Also, wet cell batteries will give off explosive gases whilst being charged and therefore need to be adequately ventilated.

As far as a low voltage cutout device is concerned, yes you should include one to stop excessive discharging of the batteries which will shorten their life. Even if discharged deeply a couple of times, a battery can be "destroyed" beyond successful recovery.

Very few fridges include low voltage cutout protection, the exception being most Waeco compressor fridges.
A low voltage protection device is only about $30 and will potentially pay for itself first use.

An Electrolux RM2310 fridge is a "3-way" fridge and the 12 volt circuit will use an element to cool the fridge contents. These are very hungry on battery supplies and should only be used on 12 volt while the vehicle alternator is providing a charge, or for very short stoppages when travelling.

In my opinion, if you intend to travel significantly, an investment in a 240v/12v upright compressor style fridge replacement will give you the best efficiency and piece of mind. Both Waeco and Engel have upright compressor fridges.

Hi Oldbaz,

so you've got a combined 130Ah of wet cell batteries.

I'd say at 30% DOD you can expect them to give you around 500 cycles, but only if fully recharged in between.
That means the alternator voltage needs to be at the higher end between 14~14.4V.
If you allow them to go down to 50% or even more, expect to get a couple of hundred cycles out of them at the most.

Based on this 30% DOD figure, they can supply 40Ah, or about 3 hours of fridge operation (13A average current on 12V).

So in theory these batteries are good for 500 stops each lasting 3 hours.
But there are other factors which you have to take into account:
batteries aren't new at this stage, alternator isn't capable of fully recharging between each stop, and last but not least batteries not receiving a regular equalisation boost.
Low voltage cutout device is definitely recommended.

cheers, Peter

Your Ctek charger might tell you if your battery is totally dead, but it won't tell you that the battery's capacity is OK.

Only one way to find out - hook the batteries up, run the fridge and check the voltage every 30 minutes with a multimeter.

Oldbaz
Do not forget to read the articles about battery's, and their "state of charge", posted on ExplorOz.
it's very comprehensive.
Cheers
Bucky