Dual Battery System

Hi folks,
Ive been having trouble with my dual battery system since the lock-down period as my van sat for quite a while doing nothing.

My dual battery isolator had stopped isolating my second battery from my main battery some years ago, yet the system seemed to work ok.

However up at Valla, my battery kept dying due to my severely shaded site and short drives with my big-ass fridge on all day/ night on a non powered site surviving off a very dead solar panel.

Hence, I bought a new solar panel and a jump starter. That was not sufficient either as my starter battery could not hold its charge.

My second battery was a a typical flooded cell lead acid which is really out of date technology.

Anyway, I could not find a lithium decent sized battery that would fit into the space under the passenger seat which I have been using for my house battery. There was one that a mate found, I checked the website and it was sold out! Very annoying.

Anyway, I managed to find a Renogy 100A lithium battery which was reasonably priced and I coupled that with a Renogy DC DC charger which is needed to run a lithium battery as they need certain charging to work which only DC - Dc Chargers can do.

Anyway, I am planning to head to Strathalbyn for the Kombi Club Bus Stop at Easter so i needed it all working.

Its not complete but it all fits and the passenger seat still fully swivels without touching the battery or the terminals.

Yet to test it camping though - the 100A/h lithium battery will go a lot further than my 65A/h lead acid house battery.

One great thing is, if you disconnect the earth, you can actually put the batter into sleep mode via its communication port - these batteries are amazing!

Pretty cool stuff! I have a 200Ah standard AGM battery under the seat, gets topped up by solar while camping and a good DCDC when driving, but the main battery tries to charge the big one when stopped, and dies!
Had to resort to a manual isolation switch, works a treat as long as I remember it :joy:

Regardless of what dual battery set up, be it lead cell, AGM or lithium, and whatever degree of battery linking sophistication, installing a separate manual isolating switch as well is your best friend. It will give you complete control with protecting the charge in your starting battery. As mentioned by naughtyG you will need to remember to switch it on and off as required. A battery monitoring device is also handy if not included in the dual battery set up.

Thanks gents,
I will have a look into a good isolation switch.
The good thing is that I can turn my lithium house battery off with a switch, but I will keep an eye on it just in case.
Cheers again.

I just remembered that my DC Dc charger does not even turn on without the ignition power input.

Hence, It switches off immediately after the engine is off meaning the starter battery stays separated from the charger unless I turn the van back on.

Hopefully that will cover this battery drain issue.

What are the dimensions of the 100ah lithium house battery? Have you modified under the passenger seat? Mine doesn’t look big enough for a battery but it is the ideal spot.

Just fits without the cover on at all and will get under the swivel seat nicely with the terminals missing the swivel base by 20mm (across). So it only just fits.

See diagram below:

Hmm, Scott if your DC DC charger shuts down with the ignition off then how does the solar input charge your auxiliary battery as my understanding is that it goes through the DC DC charger, hence the charger needs to be ‘active’ all the time, unless you have the solar panel disconnected, eg external set up when camping (not rooftop mounted).

Yes, without the ignition on I cant see how it will connect the solar to that battery.

I will have the solar charging my starter battery to make sure it copes and in the future when funds permit, I will get a DC Dc charger that has a solar input. They were double the cost of the one I bought.

I usually get powered sites and when the van is started the charger prioritises the house battery so it should charge up very quickly.

As soon as they are disconnected they seem to be able to return to 12.8V.

I watched someone test this particular battery on you tube using a heater which sucked heaps of amps from it , disconnected it and within a minute it was back to 12.8V - amazing!

I will still need a solar input version of the charger but that will keep until funds allow.

Thanks, I’ll look in to it

What brand of battery isolator do you have that has failed?

It was an SC40.
It was about 15 years old so it did pretty well for a lot of years.

Give Traxide a call. I’ve heard he is good with that sort of thing.

Thanks Phill,
It has been removed to the bin now.
It was very old and would not suit the new lithium battery.