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Dual battery / house battery -> 80 Series


Mar 14, 2016
Country Flag
I’m a bit out of my depth here so pls forgive me the newbie question:

If I have a 1994 80 series diesel with two batteries in the front, why would I want to add another battery in the rear to do the “house” stuff, like awning lights & charging gadgets & powering fridges etc.

Is it simply because the type of battery that is used to crank the 24v at start is not the same kind of battery you would use for running the “house”… or am I missing something?

Is it possible to run the “house” battery in the front, but also use it for starting??

And lastly, I can see you can get 12v air pumps for tyres on Amazon so assume that the inverter is not used for that - which means the inverter is mainly for ac type plugs (laptops/toothbrush charger/battery charging etc) - or does the inverter also get used for “house” stuff….??

The Mrs has agreed to December camping & exploring, so now taking lessons from Spain in August and raising the bar a bit so the Mrs stays keen!!
The idea of using a third battery to power "house" stuff is so the car can still be started if the third battery is inadvertently flattened or drained excessively. A deep cycle leisure battery is the usual choice for this purpose.
Yes, you could just power everything from the two main vehicle batteries but the risk of not having sufficient power left to start the engine will always be there. I'm assuming you have the 24v starting setup, hence the two batteries in the front. This can be converted to 12v starting, as has been done by some on here, by purchasing a 12v starter motor and removing the 12/24v changeover relay and other gubbins. This would then give you a "spare" battery under the bonnet to power the "house" ancillaries. If you keep the 24v, two battery starting setup I wouldn't recommend replacing either of them with a leisure battery.
There are some very good 12v compressors around for not much money. An inverter is for anything requiring 240v AC. You would need a pretty hefty inverter to power a decent 240v compressor so why bother, it's still using battery power?
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Durite do a twin pump 12 volt compressor had mine for about 6 years and paid around 55 quids should be able to get it from your local parts supplier who deals with Durite
I too went down this thought process. My conclusion was to leave the car as it was, and buy a portable power station with built in invertor for the 'house' stuff. Charge that off the car when driving, and use it in the car or around the camp when stopped. An extra battery + wiring + changes to the interior + a decent pure sine invertor + my time = vastly more expensive for no gain other than a permanent installation, which seems less flexible.

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Depending on your budget and willingness to mess, converting to 12v start makes sense for the improved starting reliability imho. It removes several components from the starting circuit that can and do fail as these trucks get old, and removes the problem of 1 dying battery bringing the other one down to it's level of uselessness. Also, if you do need a jump start, it can be done from a regular 12v donor vehicle, which doesn't always work for a 24v start. Having a spare battery under the bonnet then, for house duties, is just a bonus. You'll need a DC-DC charger to take full advantage of that bonus, so more expense and messing, but it's a good bonus and worth it imho.
Is there any benefit to a 24v starter? What was the original intent behind it?
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24v start is a cold climate (over) spec that the UK got for some reason. Batteries don't work as well at very low temperatures, and there's less voltage drop with at 24v. iirc the 24v starter is a higher kw to turn a presumably much stiffer engine at very cold temps. If everything is in tip top condition then 24v start could be a great feature in a very cold environment, but it does add complexity that most of us will never need.
Thanks Jon. Is that a similar thing that they tried to achieve with the parallel 12v batteries too?
24v starting, and electrics are generally more reliable, hence their use in commercial and military vehicles. Running 24v starting with 12v for everything else does add complexity with the battery changeover relay etc. This switches the batteries, normally connected in parallel, into series to give 24v when cranking the engine. The 24v starter, at 4.5kw, delivers more power but still draws less current than the 12v starter so the drain on the batteries is less. Toyota obviously tried for the best of both systems, 24v starting with the convenience of 12v for everything else giving a wider choice and making the fitting of optional and ancillary electrical items easier.

Edit....I might add the only problems I've ever had with mine is knackered (sticking) solenoid contacts and batteries flattened by a parasitic drain fault. In the latter case a jump start with a 12v battery to the RHS battery fired it up instantly.
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The change over solenoids fail. Not a huge problem to fix once diagnosed, and could be replaced as a precaution. There's a control module as well, but I don't think I've heard of problems with those. I think one bad battery dragging the other one down is probably the most common failure.
Thanks Jon. Is that a similar thing that they tried to achieve with the parallel 12v batteries too?

I guess they still thought 2 batteries is better than 1 if it's cold. Still has the problem of one bad battery pulling both down. On my 100 I've disconnected the DS battery from the OEM wiring and use it as a house / jump start battery kept charged with an Intervolt DC-DC charger. Much less messing on a 100 though because it's already 12v start.
Interesting info here. We in the US are terminally stuck with 12V it seems for most civil applications. I went the other way on my 80 and added (overlaid rather) 24V to the native 12V for all non-OEM devices. Partly because I wanted the runtime, partly because the cost of the wiring required to move the current demands of 24V devices is a fraction of that for 12V devices, and thus partly to keep current demands half that (or less in some cases) of 12V.
Ex, I can run both 24V air compressors on a single relay, not moving more than 12Amps. A single 12V compressor can demand 30 amps or more.