Another dual batt question

Hi Stockade,

Ive got a gel battery as my 2nd battery its an 85ah. I think the gel battery is good but an AGM is a better alternative. They can be charged at a higher amp rate and dont give out dangerous gases whilst being charged. An AGM will also lose less power over time compared to

I believe a battery around 100ah (or less) will be ok in your situation.

I would install 6mm wire as a minimum.


Cheers Wilko

AGMs are better than gel cells although very similar. Advantages. More tolerant of deep discharging. i.e. it does them less damage if they run so low, for example, that your fridge cuts out. Non spillable and non gassing. therefore safer esp. if in a cabin. Less charging reasistance. Will usually charge fuller and deeper off the alternator if that is your primary charging source. Having said all that the 'good ol' flooded lead acid is here to stay. Think Supreme, Trojan etc. You will have to make sure they are vented to the atmosphere, and they will need topping up every month or so with de-mineralised water. Treated right a good one can easily outlast an AGM and for about half the cost. However they can be a little slower to recharge.
I agree, somewhere around 100 A/H is all you need but 6mm wire is way too small. If the distance b/w primary and aux. is > than 2m. then I would suggest a minimum of 6 B&S, but preferably 2 B&S (quite heavy) Thats 13.5mm2 and 35mm2 respectively. Thicker = cable less voltage drop = much more effective charging.

If you invest in a "Flyer" battery system from Flyer from Sidewinder you get everything you need. (except the battery)

The flyer has a built-in Isolator, which protects your starting battery, sockets to connect your fridge to and the ability to charge the battery while you drive, via the supplied cables.

The reason I am promoting the Sidewinder solution is due to the functionality of the product, the fact that Derek Bester is an advertiser on this site and the prompt service and delivery you receive.

Just add an 80Ah or 100Ah AGM battery to the Flyer and you have the complete solution.
(Well maybe an accessory bracket to fix it to your vehicle's tub.)

I am very satisfied with the one I installed.


Bill.

Keeping it simple, I run a similiar 32L Engel (and 2 fluoros) overnight when camping up north Qld and use around 20-22Ahrs. This is run off a small 36Ahr AGM battery. Anything larger should be OK.

Cable size is #6 through an anderson connection.

Hope that helps,
Andrew

If starter battery greater than 50Ah (~RC90), then the easiest way for this nightly load requirement is to wire a 50Ah spiral wound pure lead/tin AGM battery directly in parallel to it, using B&S2 wire. Isolation switch is optional.
If starter battery smaller than 50Ah, then the same as above, but isolation switch is recommended.
If isolation switch is used, the wire gauge may be reduced to something like B&S6 or 8.

If no isolation switch, use a plug in type voltmeter in your ciga lighter socket for occasional battery charge monitoring.
In this case your combined battery capacities are available for powering the fridge overnight, and for starting the car next morning.
The batteries will store a useable 90Ah, while the fridge only draws 30~35Ah overnight (16 hours), and starting only requires less than 0.5Ah.
During the whole day, the fridge consumes around 50~55Ah, meaning you'll have to run the motor for 2hrs in the morning, and 1 hour in the evening (or 3 hours spread over the whole day).
If both starter and second battery were spiral wound pure lead/tin AGM batteries, you could cut the motor run times in half, i.e. 1.5 hours spread over the whole day.

There are no advantages of using a gel battery for this, only disadvantages.

A three stage battery charger for occasional topups of both batteries is recommended in both cases to extend battery life.

cheers, Peter