Lazy-person's aux battery solutions

[ilikerocks]

I'm really not wanting to install a solenoid and run a cable, and my 2007 Kia Sedona has a factory 12v outlet that's only powered when the key is on. Can I just use that to charge a small 12v aux battery? If I could, how big of a battery can I use?

 

[Optimistic Paranoid]

I'm really not wanting to install a solenoid and run a cable, and my 2007 Kia Sedona has a factory 12v outlet that's only powered when the key is on. Can I just use that to charge a small 12v aux battery? If I could, how big of a battery can I use?

As usual, the answer is:  "It depends"

What gauge is the wire going to that outlet?  How big is the fuse on it?  How many amp-hours will you need to pull from the house battery - and thus need to replace - every day.

A general rule is that a fat cable on a solenoid is going to allow more amps to flow than a thin wire to a factory outlet, so it would take longer for the outlet to achieve the same result.  Exactly the same as being able to move more water through a fire hose than you can through a garden hose.

As far as how big a house battery you can use, think of it as similar to a gas tank.  If you have a 20 gallon tank, and you use 10 gallons a day, you have to put 10 gallons back in if you want to fill it.  If you have a 50 gallon tank and you use 10 gallons a day, you still need to put 10 gallons back in every day.  If you use 10 gallons a day but only put 8 gallons back in, either tank is eventually going to run dry, the 20 gallon tank will just go dry sooner.

So it all comes down to how much power you are going to use every day, and how long you are going to drive every day.

 

[John61CT]

Ciggie ports are cr^p, IMO you must put in a proper connection for charging.

Lazy is easy, just pay professionals. Or did you mean lazy and frugal?

Define small. What average AH usage per day?

Once you are sure of the actual size you need, I would buy the battery, fully charge it on shore, then run it down to 50%.

Then at decent rpm, measure the amps when making a big-wire connection direct to the Starter battery, and how much drawn charging.

Add a 50% safety margin to the max amps measured, and that with wire length, will tell you the gauge wire and capacity of the connectors needed.

Or if you are too lazy to do that testing, just do it (or get it done) right in the first place, size it without the measuring, assuming big amps.

Unless you're willing to play with fire.

 

[highdesertranger]

remember those used amps must be replaced everyday at the very least or you will have a short lived battery. are you going to drive your car everyday? once you take the battery down to 50% it takes hours and hours of charging to get it back to 100%. just something's to think about. highdesertranger

 

[SternWake]

It will work, it will not work well. 

 A depleted battery might be able to blow the fuse to the 12v power port, and fuses, acceptable quality ones, are not cheap


Getting it to work better, would mean new wires 10AWG or thicker wire from engine battery to a 12v receptacle. 

Even better than that would be eliminating the 12v ciggy style receptacle and plugs as they have a lot of resistance, and a re a spring loaded connection which wears out, and will wear out faster the more juice it has to pass.

I'd not use more than a 12AH battery if you decide to use the stock power port.

https://www.amazon.com/dp/B001DLAO0Q/ref=psdc_15719921_t2_B004JHI8MM

And when it is most depleted, It might be able to draw enough current to blow the fuse.
A small voltmeter on battery terminals, would be useful to see if voltage rises, and how much, as you drive.

If you need more than a 12AH battery, then I'd really recommend getting thicker copper between starter battery and Aux battery somehow.

 

[DannyB1954]

You could get a portable tool system. Ryobe makes camping lights, radios, vacuums etc. Get a car charger, then you will have a lithium system.

 

[ilikerocks]

Thanks for your responses, everybody. I knew there had to be a really good reason most people opt for installing a solenoid instead of just using an existing port. I've heard of some people using a Yeti 150 (easy, but NOT frugal) with some success without the use of a solenoid. I think I may try using a <15 Ah battery, and if I have any problems I'll hire a pro to run a thicker cable.

 

[jimindenver]

What is it you are trying to run?

 

[ilikerocks]

What is it you are trying to run?

Not much... LED light, cell phone, and occasionally an e-reader. 

I just want it as a contingency so I don't accidentally drain my starter battery should I need some juice and don't plan on driving.

 

[jimindenver]

Ok what about a external USB battery pack/ power bank? Mine is 10,000 ma and could be charged back up while you are driving.

As a example this one is 10,000 ma for $15

https://www.amazon.com/GETIHU-Porta...92809094&sr=8-6&keywords=external+usb+battery

this one is twice the bank for twice the cost

https://www.amazon.com/PB-N15-20000...92809094&sr=8-8&keywords=external+usb+battery

There are a number of options

 

[SternWake]

One of those options could be as simple as buying a jumper pack, in case you wind up using too much of the engine battery, you could jumpstart yourself

When engine starting battery eventually fails from repeated deeper cycling, replace it with a marine battery.

While the jumper pack itself could be used as a house battery, my opinion would be to keep it fully charged always, and keep it for fully charged and thus and healthy, for jumpstarting duty.

If you do use it as a house battery, the internal AGM battery is not really difficult to replace when it wears out, and is likely a 12Ah or 18Ah AGM battery.

https://www.amazon.com/D5744-Sealed...e=UTF8&qid=1492840431&sr=1-2&keywords=Ub12120

https://www.amazon.com/Battery-repl...e=UTF8&qid=1492840453&sr=1-4&keywords=Ub12180

These jumper packs can be charged through the 12v power port too, but charging will be slow and incomplete leading to poor performance. They can be charged faster if actually hooked to engine battery by the alligator clamps, but this of course is not so easy to drive around with it in place.

The USB power packs rated at 10,000Mah is 10AH, but at 5 volts. that is 50 watt hours.

50 watt hours divided by 12.2v is 4.1 amp hours.

Here is a 7 AH 12v AGM battery of 17$

https://www.amazon.com/ExpertPower-...e=UTF8&qid=1492840710&sr=1-2&keywords=12v+AGM

https://www.amazon.com/AUKEY-Charge...e=UTF8&qid=1492840782&sr=1-2&keywords=12v+USB

Another option is the lithium jumper packs, and these come with USB outlets too, but again, i would save the battery for jumpstarting rather than using it as a micro house battery, but the choice is yours.

https://www.amazon.com/s/ref=nb_sb_...automotive&field-keywords=lithium+jumper+pack

 

[DLTooley]

Ok what about a external USB battery pack/ power bank? Mine is 10,000 ma and could be charged back up while you are driving.

As a example this one is 10,000 ma for $15

USB Cigarette lighter converters are common.  For some reason my amazon basics model does not work in my 2000 Ford, but works fine on the house battery setup.  I just got one of these for my small batteries, solidly built and also charges the emerging lithium technologies, including the i8650.  The LaCrosse smart(er) charger is a POS.

https://www.amazon.com/Combo-Tenerg...93168468&sr=1-8&keywords=tenergy+charger&th=1


Amp hours on these small batteries are misleading to van dwellers, the amp hours are not 12 volts.  Watt hours are a better measure to compare and you'll need to do the math to get it to 12v amp hours.

The safest thing would be to only charge batteries when the vehicle is running, including small power pack type devices.  You should consider a smaller solar setup as well.  Figuring out your estimated needs is crucial.

 

[bullfrog]

The Ryobi system worked well for us with the 18 volt lamps and fans using the in car charger and 2 extra batteries as we usually drove 2 to four hours a day while charging. We also carried a jumper battery which we never used except to recharge cell phones while parked. Lights lasted several days and fan would run 8 hours on low speed and 4 hours on high.