Camper battery question-advice please!

[mcdonaldneal]

Looking for advice here on how to get the best use out of a two battery setup for our upcoming ten week, two person road trip to Australia in a Dormobile camper we’ve owned for three years but never seen! She’s being looked after by a friend in Canberra and he is helping to prepare things for the trip.
She is a very original 1976 camper with a 55A alternator and a single battery setup to power lights, radio, 12v outlet for phone charging and a 12 litre compressor fridge between the front seats that draws about 1-3A and will run continuously. There is also a built in fridge that draws 8A when driving and runs off mains electric or LP gas when camped.
Mostly we will be able to plug into mains electricity which will power both fridges and could run a 3.8A battery charger overnight but some camp spots won’t have power and so the small fridge would use up to about 50Ah/24hrs. The other fridge would run on propane/butane and we would minimise other power draws like phone charging.

At present the battery is a 54Ah lead acid but it is a few years old and loses charge slowly and so we are buying a new 75Ah heavy duty battery. We do have a small 9Ah power pack that could be used as an emergency starter battery…

The question is: how best to wire the batteries up to maximise our power supply and to minimise the risks of running down the batteries and being stranded!
The options I have at the moment are below, please feel free to comment with suggestions and any problems in my reasoning!

Option 1: Conventional leisure battery setup with both batteries in the engine bay and a voltage sensitive relay to charge the leisure battery. The problem is that the bigger battery won’t physically fit in the leisure battery location and the ‘old’ battery has the least usable power for eg the small fridge. Advantage is the big battery will always be able to start the bus!

Option 2: Connect the two batteries in parallel, which would add together the capacity to make 75Ah+?40Ah from the older battery. On mains power the battery charger can keep both topped up with charge but I’m not sure if the two differently aged batteries will work well together? This gives max capacity but if they did both run down then we need the emergency start power pack…

Option 3: buy a battery box for the new 75Ah battery which has a 12v output and USB sockets for phones but would not be able to charge when driving (and crucially will not fit in the engine bay and so takes up valuable storage space in the living area). The old battery can stay as the cranking battery. The main problem here is that the battery box might not always be at full charge for off grid camps.

I favour option two but I’d like to hear anyones advice and opinions!
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1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[mcdonaldneal]

Olive Dormobile Kombi thread

Some pics for interest!
Olive, our Dormobile camper, the 15L console fridge between the seats and the kind of battery box I’m talking about:

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1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[Abscate]

I’m still not quite clear on what hot draws will be but I would not parallel different batteries types or ages.

One thing to bring to your attention. You can get a two battery independent charger ftom a marine chandlery rated from 4-10 amps each. That would let you top off each battery ftom shore power without worries

54 amp hours. Per day will need charging each night and is hard use. It will last for 10 weeks though!
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.ssS!

[mcdonaldneal]

[mikedjames]

I would start a 10 week trip with two new batteries. Go a bit bigger on the starter
. A 65AH car battery will fit.
And buy a higher capacity leisure optimised battery .. a 100AH or 110AH leisure battery fits under the spare wheel tray in my bus. It can start my 1641 engine if needed but its not able to survive doing it regularly. You lose plate thickness and gain plate area in a leisure battery.

In a new to you vehicle theres going to be enough learning without adding worries from batteries dying on the trip, as no doubt that weak starter battery will die inside 10 weeks.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[Abscate]

Ah! Your Dormobile is a manual so you can always start it with a push, too!
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.ssS!

[Starbucket]

I would buy a small (1000 watt) gas generator with 110V and 12V outlets to run things while camped and to keep things charged and for a quick charge if you run the batteries down over night. A 100 watt solar panel or two would help also.

[Slip356]

I have a 1000 watt Honda generator and an extended 5 gal marine fuel tank with fittings that connect the tank to the generator. Have a long heavy duty extension cord so I can move the generator well away from me or other campers. Chain it to a tree. Will power everything in the bus, fridge, small electric heater, radio and keep both batteries fully charged with a dual battery tender.
Will run steady for several days/nights on a single tank. Have had this setup for over five years and it’s perfect. Even bought the generator used ten years ago. Added the extended tank as got tired of getting up in the cold to refuel the generator at 3AM. I do quite a bit of cold weather camping.

[Abscate]

Keep it simple for 10 weeks.

20 amp hours is three days between charges, and use ice to bridge thst longer. You could easily go a week between shore charge with that plan

Phone charge loads are nothing in your budget.

Keep a simple charge pack for emergency starts and phone charging.
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.ssS!

[mcdonaldneal]

A generator would be cool but I’ll count it out in terms of noise and storage.
I hadn’t really thought of ice to bridge a gap (we’d never take it on a camping trip in Scotland, for obvious reasons!)
I’m almost certainly overthinking the issue. We do have a power pack for emergencies, so it’s likely we’ll go with the one new battery, or possibly if we get one that fits in the leisure battery spot, two identical ones linked together (but that feels like overkill for our modest needs!)
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1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[Mberglo]

I went with a second battery and circuit with built in switching relays. Since this build, I've swapped over to a LiFePO4 battery, which provideds twice as much capacity and half as much weight.

https://www.thesamba.com/vw/forum/viewtopic.php?t=754156&highlight=

[metahacker]

I like option 2 but I'm not so sure about your situation with regards to existing battery chemistry and age. You can use a (cheap) Victron Smart BatteryProtect to both monitor voltage (bluetooth app on your phone) and keep them from going flat.

You can also observe their "interaction" a bit by charging them up and then disconnecting loads and watching the Victron SBP voltage level at rest, to see if they end up going into some death spiral being connected together.

People over-stress the whole connecting dissimilar batteries thing.. the main thing, as long as they are both in good shape, is just the chemistry (and thus voltage vs %SOC curve). Yes, it's ideal to use a 100% matched set in your bank...but can dissimilar batteries of simply the same chemistry work "fine"? Yes...

If I wanted to pick the "best" two batteries to put in a Bus it would be 2 x Aolithium 100Ah LiFePO4
https://www.amazon.com/gp/product/B09CDKYMTP/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
One on each side of the engine bay
Connected directly

Put a Victron Smart BatteryProtect on the circuit before your fridge and any other accessories (except for ones that are capacitive - e.g. your inverter, which should have it's own voltage sensitive disconnect). Set it to something conservative like 12.0V ...

Voila, ~160 - 180Ah of real usable capacity. (keep in mind SLA/AGM will really only give you maybe 50-60% of the rated Ah in real service, if you don't want to damage the batteries.. and LFP will give you basically 100%.. while weighing a fraction).

No matter what setup you end up with, a compact, low-cost, flat-foldable portable solar panel is a good idea to have:
https://www.amazon.com/gp/product/B07ZZ5SRJ6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

[mcdonaldneal]

Thanks. Some good info there, I hadn’t really realised the potential for using LiFePO4 batteries-looks amazing but probably beyond budget for this trip.
I have a portable solar charging setup for camping in Scotland and see how it could be useful in Aus. I’ll keep it in mind.
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1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[mcdonaldneal]

Just to finish off this thread:
I ended up choosing an 85Ah dual purpose cranking/deep cycle battery and will run it as a single battery setup. It’s possible we’ll take the old battery as a spare but maybe not.
The new battery is wider and taller than the older one, and weighs 26kg and the terminals are reversed. The mechanic wasn’t best pleased to have to manhandle it into the tray (painted the inside of the battery tray first) and fit a longer earth cable.

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1978 marino yellow Bay Dormobile camper
1969 signal orange Karmann Ghia convertible
1976 martini olive Bay Dormobile camper

Stop dead photo links! Post photos to The Samba Gallery!

[airschooled]

Very nice! I live 5 months a year off my 55ah dual-purpose battery with 200w solar. I think you'll be pleased, and your engine appreciates the weight savings of a single battery setup.

Robbie
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