Hi all,
We've been using the fatty for camping a lot recently, despite being tempted by those fancy Jackery type devices I'm kind of tight and I think whacking a 100aH AGM into the boot compartment and having the cigarette lighter socket powered from it is a more economical option!

To that end, I had a look around at various intelligent systems to allow the secondary battery to charge from the main, these kits seem highly recommended and will do what I need, I think...
https://www.bluesea.com/products/7650003/A...5BBoxed%5D

Some questions though:
1) Would this work with the smart-alternators fitted to these cars? It's going to need >30 seconds of 13.6v or above to start charging.
2) Is 120A enough? I've a feeling the alternator is 150amp, but I've not been able to confirm this (google fail).

I'm thinking I'll eventually stick a couple of cheap 100watt solar panels on the roof through a MPPT controller to charge the secondary battery when stationary. But one step at a time!

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Last edited by Phoenix on 23rd Dec 2023 9:43pm. Edited 1 time in total

A possible even simpler solution is to wire the auxiliary battery to the 100A cable at the rear fuse board and earth directly so it is permanently in parallel with the front battery and then fit a manual battery isolating switch to the front battery -ve cable.
The two batteries will then always be charged, when you get to your campsite or where ever simply switch off the front battery to keep it fully charged until you need to start the engine.
Had this set up on a Discovery and now this car for about the last 20 years, never had an issue.

Phoenix wrote:

That seems a lot of complexity for a simple problem...
Use a Durite 140A split charge relay to charge the aux. battery, then have a manually switched Albright 180A relay (don't worry about the rating, that's continuous not short-term) in parallel, the coil obviously needs to be powered from the aux. battery. Run a bit of 5A wiring to the drivers footwell and repurpose the transit switch (momentary, so you need to hold it on) to trigger the 'jump start' relay as required.

I used a similar voltage sensitive relay on my Discovery 3 which has the same charging regime and it worked reliably for years so I wouldn't worry too much about the charge voltage control.

nicedayforit wrote:

A possible even simpler solution is to wire the auxiliary battery to the 100A cable at the rear fuse board and earth directly so it is permanently in parallel with the front battery and then fit a manual battery isolating switch to the front battery -ve cable.
The two batteries will then always be charged, when you get to your campsite or where ever simply switch off the front battery to keep it fully charged until you need to start the engine.
Had this set up on a Discovery and now this car for about the last 20 years, never had an issue.

There's a 2-way rocker switch in the middle of the front edge of the drivers footwell finisher, it's used to trigger the transit relay, which is removed at PDI. The switch is effectively redundant (but has power to it still) so you could either repurpose that or have a 'hybrid' solution with the split charge relay and a manual isolator switch as suggested above, that way you wouldn't have to remember to disconnect when parked, you'd only have to close the isolator terminals when required - and I was assuming you'd be using the existing wiring back to the starter battery from the rear fuse box.

Just had a look, doesn't seem to be one on mine - can see a hole where it probably was, but it's been removed (FWIW, it's a German market LHD vehicle).

Probably not a big deal anyway tbh. In an emergency a jumper cable to by-pass the relay would do the job! It's not something I intend on needing to use very often!

Other difference seems to be the Durite isn't dual-sensing, so it won't charge the starter battery when the solar panels are being used.

Not sure whether that's a deal-breaker either tbh, I'd primarily want to be keeping the leisure battery topped up for running the fridge and other stuff, the starter battery generally doesn't need charging (assuming everythings working as normal).

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Last edited by Phoenix on 23rd Dec 2023 9:44pm. Edited 1 time in total

I’m thinking of putting about 200 watts worth of panels on the roof rack, with an MPPT controller to charge the leisure/aux battery.

I want enough to be able to keep a small fridge running for a weekend or longer (longer than a weekend we’re likely to be driving the car to keep it charged, or to have an electric hookup).

In my experience, an Optima Yellow Top would run an Engel fridge at 2 degrees C. for >26 hours before the low voltage relay cut-out at 10.8VDC
Now a D34 is only 55Ah (but has deep discharge and is great for fridge and winch-equipped vehicles) if you can fit a 100 or 110Ah aux. battery and it's just to run a fridge, providing the maths confirm it - do you really need the solar panels if it's just <48 hours between alternator charge cycles?

What you are after is the same as I have had. I have a 100a battery in the rear area with the terminals connected to an Anderson plug and a 100a resettable fuse. On the car, connected to the rear fusebox feed is a simple voltage sensing relay wired to an Anderson plug. When I am driving the 2nd battery is connected to the car via the Anderson plug, when stopped camping I disconnect from the car and connect a 200w solar panel through an mppt controller. The aux power socket in the rear of the car is disconnected from the car harness and connected to the 2nd battery. I plug a Fridge Freezer into the Aux Socket. This set-up allows unlimited days away off grid. This is a duel sensing VSR. https://www.kickassproducts.com.au/Battery...dAQAvD_BwE



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Phoenix wrote:

In my experience, an Optima Yellow Top would run an Engel fridge at 2 degrees C. for >26 hours before the low voltage relay cut-out at 10.8VDC
Now a D34 is only 55Ah (but has deep discharge and is great for fridge and winch-equipped vehicles) if you can fit a 100 or 110Ah aux. battery and it's just to run a fridge, providing the maths confirm it - do you really need the solar panels if it's just <48 hours between alternator charge cycles?

That's why I'm doing the battery first, will see how it pans out - we'll be using the battery to charge other bits and bobs too, so I suspect we'll be close to using the available capacity. I don't have the fridge yet so I can't do any realistic calculations (from what I've seen on YouTube, 1.2kWh's is enough to run one for 40 hours, but, y'know, YouTube science

Best I think I can fit so far is about 85aH, if my measurements are correct I can squeeze this in with enough room for the cabling: https://www.batterymegastore.co.uk/product...tery-xv85/

wayneg wrote:

What you are after is the same as I have had.

You probably won't want the expense of my battery, It's an Oddessy Extreme pc1700. It's over 10 years old now and still load tests at over 1070cca. If fits in the boot space with a little room to spare. Also you can lift the loom out and re-route it over the fusebox. I would not risk the chance of the battery rubbing through it. There is also a stud in the bottom of the hole that needs to be cut off. https://www.odysseybattery.com/products/ods-agm70-battery-pc1700/