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Contemplating: Second Battery in the Car

Discussion in 'Survival/Preparedness Forum' started by Bolster, Jun 1, 2012.

  1. Bolster

    Bolster Not Ready Yet!

    Jul 23, 2011
    State of Stupidity
    I have been contemplating a second battery in my vehicle. Been contemplating it for some time, but never done anything about it.

    My inaction is due to the sad state of my electrical knowledge. I neither know how to add a second battery, or if it will even yield the benefit I hope.

    What I want -- is that I have considerably more Ah to spend while the engine isn't running, for using a (ham or CB) radio, or recharging electrical devices, using a computer, etc. So, another battery in parallel (obviously want to retain 12v). And as a side benefit I'd like to be able to start from the secondary battery if the primary fails--or at minimum, to recharge the primary from the secondary. (Although I've read that deep cycle can be used to start engines.)

    But this brings up a load of questions. Do any of you have experience here?

    -- Would the second battery be like the first, or would it be a deep cycle battery? If a deep cycle, will it play nice with the standard battery?

    -- Would I need to get a larger, beefier alternator, and what would that do to MPG?

    -- Would I be able to isolate the 2nd battery so leaving a light on overnight would not discharge both?

    In general, what are the pros and cons of adding a second battery to a vehicle? I would like to make my vehicle a bit more useable as a bug-out option. And it seems that "more electricity" would be a good start.
    Last edited: Jun 1, 2012
  2. Dexters


    May 3, 2004
    Last edited: Jun 1, 2012

  3. G29Reload

    G29Reload Tread Lightly

    Sep 28, 2009
    Optional extra juice is always good.

    Problem is, larger batteries do at times need ventilation.

    So, that means engine compartment, limited, claimed space there.

    You could try an independent system.

    Maybe a motorcycle sized battery.

    Case it in a wood container you build yourself, with a 12v charger/regulator. Have it sit behind the front seat. Have a wire running from the batt charger to a 12v plug you stick in the cigarette lighter, manually, when you're driving. Ability to hard-disconnect it just by yanking so you don't endanger the main engine battery.

    Run lights or whatever, off the independent MC battery as a compartment light if you were bugging out and sleeping in the vehicle. efficient LEDs. 12 equipment to charge your cellphone, VHF, whatever.

    Adopt a maintenance discipline to keep your battery in the vehicle charged and monitor it more. Own a battery charger, I just bought one, its something good to have. Use it to top off your MC batt.

    Batteries get killed by cycling down too far too often. If they stay topped, they last longer.

    Also, look at individual added capacity for your dependent devices. Company called hyper something or other, for example, makes nice iphone cases that contain batteries that double the talk time. They look like ordinary wrap around cases, but they're plugged in to phone when you put them on.

    Well not hyperjuice, those are externals, but someone else makes them.

    If you have a traveling notebook, keep that charged up with add on batteries, use the NB to charge USB externals.

    phone, ipod ipad, etc. notebooks.

    For your HAM WT, most have aux batts you can buy…spares.

    Lighting, you may also go to a battery powered lantern, just find one with high efficiency.

    for remote camping, you could also look at a solar re0chargeable kit for the MC batt project I suggested.
  4. Bushflyr

    Bushflyr ʇno uıƃuɐɥ ʇsnɾ Millennium Member

    Mar 17, 1999
    Western WA
    You can do what you propose, but IMO it's not worth the hassle and expense for a BOV. Many trucks, particularly diesels, have dual battery setups for more cranking power. These are different than a camper type setup where you have a separate deep cycle that charges off the vehicle but is isolated in use.

    First question is what type of vehicle and do you actually have space for a second battery? Next, is the expense and trouble worth it? You can buy an EU2000i used for $400-600. Roughly what you're looking at for a spare battery and the wiring to do it correctly. Do you really need to run your computer off of your vehicle battery? If you decide that it's yes to all, look at a camper deep cycle type setup. Your MPG won't change significantly, but you will need to make sure your alternator can handle the extra load of charging both batteries. The margin on modern cars can be a little tight.
  5. Bolster

    Bolster Not Ready Yet!

    Jul 23, 2011
    State of Stupidity
    Wow great replies already, thanks.

    Yeah, assume I have room in the engine compartment. (It's a pickup I'm thinking of modifying).
    Last edited: Jun 1, 2012
  6. G29Reload

    G29Reload Tread Lightly

    Sep 28, 2009
    Looks like a great read:

    [ame=""] The Battery: How Portable Power Sparked a Technological Revolution: Henry Schlesinger: Books@@AMEPARAM@@[/ame]
  7. NDCent

    NDCent Socially Inept

    Mar 19, 2010
    You need to google battery isolators...

    You're wanting them isolated and also hooked in parallel, if I'm reading it correctly. I believe you will need a manual disconnect installed along with an isolator to be able to do both/either on demand.
  8. G29Reload

    G29Reload Tread Lightly

    Sep 28, 2009
    Also you might consider buying one of these:

    [ame=""] Duracell DPP-600HD Powerpack 600 Jump Starter & Emergency Power Source with Radio: Automotive@@AMEPARAM@@[/ame]

    I've also thought about getting one of those solar chargers that sits on your dash, a solar panel.

    Feeds to your cigarette lighter to trickle charge your cars' unit.
  9. Ten years ago I did what you're proposing to a Dodge mini van.

    Installed a large mixed cycle battery right behind the drivers seat in a plastic battery box. No room in the engine compartment. Hooked a 300 watt inverter to it for 120 volt AC. Hooked lights & 12 volt outlets to it also. Everything coming off of the battery I ran through a small fuse block.

    Used a manual disconnect to isolate it from the van's electrical system. No other isolation is needed. The disconnect was normally closed so the two batteries were tied together. They both started the engine.

    I spent the night a couple of times in the van and to keep warm I used an electric blanket plugged into the inverter with the disconnect open. The blanket would pretty well run the battery down. Lights would be dim.

    Then start the van and close the disconnect switch. The regulator that came with the 3.0 V6 would charge both. Did it no harm, just takes it a while.

    Used both batteries for almost exactly ten years until they died and got replaced. The whole system is still in place and still working fine.

  10. janice6

    janice6 Silver Member

    Apr 4, 2006
    I ran a minimum of 160 or 180 Watts mobile. I also spent two hours of rush hour in city driving, each way. I used a single battery but replaced the Alternator with a minimum of 115 Amps and it's companion regulator.

    I had to make sure the drive belt was tight all the time because when transmitting from a stop light, the power requirements were so high the belt to the Alternator would sometimes slip trying to come up to speed.

    The key was to have an alternator that had a high enough output that it was still charging at idle rpms.

    I had great success. I had not used dual batteries since my first cars that used 6 Volt batteries, and that was only because of "Winter starting" problems at 20 to 30 below zero.
  11. Bolster

    Bolster Not Ready Yet!

    Jul 23, 2011
    State of Stupidity
    Now that's what I'm talking about! Inspiration! Sounds like it works great.


    Mar 3, 2010
    I run a 12v fridge in my rig when we are camping or off-roading. I was able to swap out the 650cca battery for the 900cca one with way more Ah with no modifications. Then I have a smaller solar panel with a 12v plug that I plug into the cigarette lighter to keep the battery juiced up. It seems to work pretty darn good.
  13. Bolster

    Bolster Not Ready Yet!

    Jul 23, 2011
    State of Stupidity
    Would that be a Peltier Device or a genuine refrigerator? And you didn't switch out to a deep cycle battery?
    Last edited: Jun 1, 2012
  14. Jumper


    Jun 10, 2002
    MI USA
    I did something similar a few years ago to a Chevy Tahoe. It had a system that needed to be powered when the engine was off. I used two deep cycle batteries but I suppose you could use a single standard battery also. I used a type of relay that automatically broke the connection from the aux batteries to the main battery if the aux battery voltage dropped below 11.5 volts (i think). This was a failsafe to prevent the auxillary batts from draining the primary battery.

    It was easy with the Tahoe because it had a heavy guage wire that ran to the trailer electrical connection at the rear of the vehicle and I just tapped into that. The Tahoe had a towing package that was meant to charge a battery in an RV while it was trailering. I'm sure other vehicle's do to. Your truck may have something similar. I would think that most RV dealerships would have the knowledge to help you with this setup. Thats where I went to get my system set up. I still have the relays now that I think about it.
  15. RED64CJ5


    Jul 7, 2003
    Read this entire page. It is very, very informative. Many hams uses K0BG's site as a reference for all mobile installations:
  16. Bolster

    Bolster Not Ready Yet!

    Jul 23, 2011
    State of Stupidity