Adding a third battery (configuration)

[DWWood]

Hi,

Not sure where to ask this question or even if this is the right forum but I have a Hilux so though I should start here.

I have a Projecta 25A DC/DC charger mounted to a battery box that charges a 105ah Full River AGM battery (photo - Battery 1). The battery is charged while I drive via the alternator and when camping I plug in a 160 watt solar panel to run a couple of fridges, everything plugs into the box on Battery 1 and everything works as it should.

Recently I acquired a second 105ah Full River AGM battery (photo - Battery 2) and had it wired via Anderson plug to double my usable power (photo - Batteries) which is basically just ran as a stand alone battery as in nothing is connected to the battery except 'Battery 1'.

I'm hoping someone can help me with a couple of questions;
1. Will the DC/DC Charger be charging 'Battery 2' in it's current configuration?
2. Is this the optimal way to charge both batteries or should I swap the DC/DC charger to Battery 2 and leave the fridges to draw from Battery 1?

Any help would be appreciated.

[martynvella]

If it is connected in parallel to batt 1 it will just act as one large battery and share the load and charge.

If you can it is best to have a relay to supply your fridges direct from the start battery when the engine is running so the dc dc charger is devoted to charging the batteries and not getting confused by the fridges switching on and off but as i found this can lead to problems without a delay timer.

[OffLineR]

If both batteries are not on the same spec they will drain each other.
So whenever you are not chargingt them you need to seperate them.

If they are connected paralel they should be charged the same as well.
Maybe they will equalize first than start charging due to same reason I have mentioned above.

[OffLineR]

So are you happy with the DCDC charger?

[DWWood]

So are you happy with the DCDC charger?

Yep, very happy with the charger. Hasn't missed a beat.

Batteries are both same size and same manufacturer. I asked the question to Projecta and he said set up is fine but for proper charging the positive should be on the + terminal on battery 1 and the negative to - on battery 2 but as this is a portable set up it wouldn't be ideal.

[martynvella]

That is just being anal. On paper it looks practical but in the real world makes negligable difference. Might make about 5 minutes difference to the charging time from fully discharged.
All the armchair experts bang on about this sort of crap in forums and everyone eventually starts to take it as fact.
Even cable size is way over hyped in forums. When your batteries are right next to eachother as yours are 6mm automotive cable will be more than sufficient but some will tell you to use anything up to 3B&S on some forums.
Fact is with cable resistance is in length so in your case the difference between 6mm and say 6B&S ( roughly 3 times bigger at a guess) would be close to zero with charge time, but if the batteries were 10 metres apart would be significant.
What you are doing is fine as long as both batteries are servicable so include a method of removing either battery from the system if it fails leaving the other to run everything.