Second Battery query

I know this has been a previous topic but the references in the posts re batteries may be out of date.
Can anyone suggest a suitable battery which fits in the battery compartment behind/under the the passenger seat?
I have managed to squeeze in a VARTA 44 on the other side as my starting battery.
I have never had one but believe I need a deep cycle battery as an auxiliary battery.
Thanks for any suggestions
'89 Syncro, Adelaide

Check out the array of lithium deep cycle batteries - they’re smaller in size, longer lasting and substantially lighter in comparison to other types of batteries BUT unfortunately they are expensive!

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Oops, forgot to mention they can be placed on their sides and even upside down.

Hello Peter. many of us have been down this path. If you run a fridge or other electrics, a house battery is essential. I installed a swivel seat to give a little bit more height and there were a few batteries around that would just fit. I did have a varta and then swapped to one from a guy in Brisbane. But I went for something a bit bigger and now have a good “kickass” brand slim line 120 ah one under the rear seat. It’s not a lithium because my budget would not run to one but that would be my preferred option. I run a waeco fridge, water pump for sink water, recharging mobile phones and LED cabin lights. It lasts me a long time. I have a solar blanket to charge it up during the day when we are camping. I have the auxiliary battery connected to the car battery through a gadget that cuts out the connection if there is a risk the car battery is getting too low. If you have the cash, and still want to fit one under the passenger seat, check out the variety of lithium batteries on the market.
Cheers, Peter

Hi Peter L,
I have done a similar thing to Peter C with the swivel passenger side seat which allows for additional height clearance for a house battery.

I had a Varta battery which cleared ok yet was only 60A/h and a lead acid so it didn’t last long when running my monster fridge after a cloudy day when the solar panel didn’t really do its job.

I have since upgraded my solar panel to a 200W foldable version and just upgraded the house battery to a Renogy 100A/h Lifepo battery which has yet to be tested camping. The great thing about these is you can put them to sleep like they are disconnected yet keep the terminals on. There is a plug in cable with a switch on it to turn the battery on - very easy.

Like Peter my solar is set up to charge my standard lead acid starter battery only and when I turn my van off the house battery is separated completely from the main battery via the Renogy DC DC charger. As soon as the ignition is switched on, the alternator will charge the house battery to its maximum voltage and then cut off charge until it drops again.

This is the thing - if you get a lithium battery, you really need a DC-DC charger or you might over charge and overheat the lithium battery which can cause damage to it.

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Also looking to go down this path mainly to free up some space under the rear seat for speakers and perhaps a diesel heater. Do you have the Renology model number to hand @kombi4x427lc ?

Hi Jon,

The battery has the following code on it:


That should get you where you need to go to grab one.



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Hi guys. I went lithium as well. Renogy 170ah. I shouldn’t need solar. under the bed seat with their 50ah dcdc.

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Seems to be the brand to go for. Decent value as well.

Does that 50 amp DC to DC charger cause any issues when the battery is flat? From what I have read lithium batteries will take as much power as you throw at them (so assume 50amps in your case).


Jon. I haven’t flattened the battery.
The dcdc I think is somehow limited if you have solar connected. But with 170ah in assuming it’ll last a while even without solar. We just have the basics, fridge lights, fan, water pump etc.
It’s never been below 13.2v. I don’t look at the amp draw.

I’ll have a look at my emails. I might have s discount code you can use. Delivery was good. Packaging is good. I’ve also got 3x 100ah in my boat.

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Only issue is with a 50A DC-DC is the high current it draws from your alternator!
Our alternators are only rated @ 90A. A DC-DC charger draws probably 30% more than its output , means @50A it will be around 65A. That leaves 25A for the rest of the car. The more it draws, the hotter the alternator gets. At low engine speeds, there may not be enough airflow provided to keep it at an acceptable temperature and it may burns out.
Other thing to consider is the right size of wire to run to reduce voltage drop to the DC-DC charger. Which size is recommended depends on wire length, voltage and how much power draw is applied.

Just something to consider when you install a Lithium system. Bigger is not always better :wink:

In light of what Arne has written you could consider a stronger alternator such as the Syncro campervan purpose built 175 amp alternator from Campervan Culture. I have a similar set up as you re lithium aux battery and DCDC and with the 175amp alternator - no issues. BUT, the alternator is expensive!

As I only installed a 100Ah lithium battery I went for the 20A DC-DC charger. They basically say use the DC-DC charger that matches you battery as recommended by Renogy on their website.

I have a larger alternator than stock in my subie syncro as my original one failed so I upgraded - that was all that was in stock anyway.

The lower amp draw and the higher rated alternator should keep my system alive - hopefully!

Nice! I didn’t know these existed.

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My setup. Upside down. Sorry