Can a jump starter battery be used as a spare caravan battery?

Buzz Lightbulb · Guru

Can a jump starter battery be used as a spare caravan battery?

darjak · Senior Member

Most good agm batteries can be used as both.
Ive been save a few times in first vehicle we owed, were in the middle of nowhere
every time with van hooked up. Had it set up with a Redarc isolater with a push button
bypass on the dashboard running 6BS cable.

PeterD · Guru

Whilst modern jump starters can supply a large starting current for a few seconds of time they do not have a great capacity that can be used over a long period of time. Many of them I have seen only have a capacity of 20 Ah or less (generally expressed as 20,000 mAh to make them look good.) You could possibly use them for a few lights for the night but forget about running a TV or car fridge for a reasonable period of time.

Whenarewethere · Guru

As said above.

When looking at a battery go to the manufacturer's data base & look at the battery specs.

As I couldn't fit another full size battery in my car, I went for four 26Ah batteries that will mostly fit.

The advantage is that 4 of them in parallel can provide huge amperage for jump starting. I have also wired in 175Ah Anderson plugs for jump starting.

Screenshot_20210320-175826~2.png

Whenarewethere · Guru

If you have been using your jump starting battery as an auxiliary battery. Then you need to be able to charge that battery up if both are flat. Some solar input is probably the easiest solution, but you probably have that anyway.

Craig1 · Guru

My NoCo (V8 diesel start rated) has a variety of lighting options, I assume for a fairly short time, and a usb output which would charge a phone. But no good for running a van me thinks.

Whenarewethere · Guru

Cars these days are stuffed full of electrical gadgets I would avoid using the starter battery for anything.

Simply opening a door while camping will fire up the car's circuits thinking you are going to drive off. You will be shocked how many time you do this in a day while camping next to the car.

Having backup & charging options is a lot of peace of mind.

Buzz Lightbulb · Guru

Whenarewethere wrote:
Cars these days are stuffed full of electrical gadgets I would avoid using the starter battery for anything.
Simply opening a door while camping will fire up the car's circuits thinking you are going to drive off. You will be shocked how many time you do this in a day while camping next to the car.

Having backup & charging options is a lot of peace of mind.

Are you suggesting that I shouldn't use a jump battery to start the car if the car battery goes flat?

Mike Harding · Guru

Darjak's reply is correct.

An AGM battery of 60Ah+ will be able to jump start most vehicles. However; the problem you will encounter is establishing a sufficiently low electrical resistance connection between the two batteries via jumper cables this especially so with diesel vehicles. I have no simple answer to that problem.

Whenarewethere · Guru

Don't use the starter battery to run stuff when the car is off.

I have jump started 1 car this year, 2 last year.....

Whenarewethere · Guru

Mike Harding wrote:
Darjak's reply is correct.
An AGM battery of 60Ah+ will be able to jump start most vehicles. However; the problem you will encounter is establishing a sufficiently low electrical resistance connection between the two batteries via jumper cables this especially so with diesel vehicles. I have no simple answer to that problem.

I have welding cable & have the option of keep the cable short. Also the clamps are solid copper, not copper plated.

PeterD · Guru

Buzz Lightbulb wrote:
Whenarewethere wrote:
Cars these days are stuffed full of electrical gadgets I would avoid using the starter battery for anything.
Simply opening a door while camping will fire up the car's circuits thinking you are going to drive off. You will be shocked how many time you do this in a day while camping next to the car.

Having backup & charging options is a lot of peace of mind.
Are you suggesting that I shouldn't use a jump battery to start the car if the car battery goes flat?

He said nothing of the sort. The words "Having backup" in the last sentence includes the use of a jump-start battery.

Jaahn · Guru

Hi Buzz smile

Possibly the thread has wandered off the point. aww

A simple answer is YES you can use a jump starter to power your caravan as a spare battery. BUT you do need to have a battery that is big enough to do what you want. The small lithium jump starters are good for quick burst starting but their actual capacity is very small and would be flattened quickly by continuous use. So a AGM battery of a reasonable size could suit both purposes if big enough. hmm

BUT if you use the power in the caravan it may not be able to jump start a car until it is charged up again. No free lunch there ! I carry a (double) battery jump starter as insurance for going where I want in the bush with an automatic. It can be wired as 24V for a truck MH that I had previously. I do use it as a portable power source for things like lights and TV etc as it has a 12V socket on the box. It gets charged off the solar when needed. I use two removable short leads with clamps that I removed from a good quality battery jump starter that died. I have wing nuts on the external battery power lugs to attach the leads for jump starting. As said before I have jump started quite a few cars over the years but never had to do mine yet. biggrin

Jaahn

-- Edited by Jaahn on Thursday 1st of April 2021 03:23:45 PM

Whenarewethere · Guru

I have an Anderson plug next to the starter battery & auxiliary batteries.

Short & longer jumper leads (ends which can be use conventionally) & Anderson extension lead. The extension I can use to self jump start, or with 175 to 50amp adaptors use for a desperate extension on the solar panels. The clamps are Utilux 200amp continuous 2mm thick solid copper.

I have never had a flat battery. A DC clamp meter is a really useful tool to check amps.

Heat gun works really well for soldering heavy cable & at a lower temperature to shrink heatshrink tube.

Whenarewethere · Guru

A few years ago the neighbours came to me panic stricken. A flat battery, no jumper leads, no other options & they couldn't wait for road service as they were in a bit of a hurry to get to hospital to have a baby!

Bicyclecamper · Guru

"20 years ago, I had a Lion 20 ah Jump Starter, and we used that as our c,van battery, for 5 years. I would charge it in the car, every second day. We used it for lights, to run the tele, and run a radio. It died after 17 years, and the next one I have bought from another Company much dearer, is only 3 years old, and I don't think it will last as long. They are/were also used as a Jump starter.

PeterD · Guru

Rick, Don't expect your current jump starter to power your accessories for any near the same time as the old one did. Jump starters don't necessarily need large batteries to start a vehicle. They just need batteries with a low internal resistance to do the trick. You don't need much power to start a vehicle. It only takes a couple of seconds on the starter to start a vehicle that is in good condition, one in poor condition may take 5 seconds (or 1/750th of an hour.) One of the larger diesel engines may require 600 A of current to start it. If the motor takes that long you will only consume 0.8 Ah from the battery.

20 years ago jump starters used different batteries, they were lead acid types, both of GEL and AGM construction. The modern jump starters contain lithium batteries. Lithium batteries Have a far lower internal resistance so they can be much smaller to deliver the same short term current. If you could build batteries with a low enough internal resistance, you could start a vehicle motor with 8 torch batteries.

That is why I say you can't use a modern jump starter to provide much power to power accessories in a van. This link shows a range of jump starters. If you go through them you will see the range of current capacities. I did not go through the lot but the highest I found was this one - 18 Ah. You won't power much in your van with this one.

Whenarewethere · Guru

I videoed my clamp meter while starting the engine.

238 amps for 1 second, then straight away it started charging at a modest amount. The car's computer must have checked conditions, then 30 seconds later up the charge to 80 amps. After a couple of minutes I took the clamp meter off.

12 volts x 238 amps = 2856 watts / 60 minutes / 60 seconds = 0.79333 watt hours. Or 0.00079333 kWh.

2.0L petrol engine with a 1 year old starter battery.

Let's say you have a large diesel engine. Even if you need 3 time the energy, it's still next to nothing.

Pocket jump starters just need to give a powerful quick whack.

dabbler · Guru

Jump starter stored capacity is tiny by most standards. At 43ah, my AGM based jump starter is a poor substitute (or supplement) for the 280ah I have in the ute tub or the 180ah I have in the TD. I imagine most people would be in the same relative position. I have the recharge capability for the jump starter and have used it to power things in camp. I decided not to permanently cable my aux setup back to the cranking batteries but I carry everything necessary if I'm well and truly stuck.