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Home Forums General Discussion Deep Cycle Battery charge from my car?

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    I travel 1 1/2 hrs daily to work. Thought I could put a bank of deep cycle batteries in the trunk to charge off my alternator, and then run a small refrigerator and 12V lights in my small home in the eveings. Will this work? Anything I have to consider? Thanks.


    How big is the battery and how big is the alternator? It probably will work but if you totally discharge the battery ever night will the alternator recharge it in the available time.

    Second thing to consider is whether the charge current demanded by the discharged battery exceeds the capacity of the alternator. You may simply end up burning out the stator windings. Are you driving a small Honda civic with a 30 amp alternator or a big Detroit car with a 90 Amp heavy duty alternator?


    There are too many variables for a clear answer, but elnav has given some good info. It’s nice to use the “free electricity” created by your car. One thing that would help would be a low voltage disconnect. That way you can be sure the car will start in the morning and you are not late to work!

    I use old fashion kerosene lamps for light and a propane fridge from a camper. I can always count on them to work.

    Good luck!


    get a split charging relay installed in your car this will resolve your issue see link for a good overview any good auto electrician can ins0-727-23, DURITE 12V, 70A-20A SPLIT CHARGE RELAY

    Durite 12V 70-20A split charge relay,

    For 12V application,

    Rated 70A-20A at 12V DC,

    Isolates fridge circuit separately,

    2 x 2.8mm blade terminals,

    1 x 6.3mm blade terminals,

    2 x 9.5mm blade terminals,

    Quality replacement for:

    Lucas: SRB630.tall this.


    yes its possible here is what i did and yes i have used this setup

    a lot over the years


    too many batteries WILL put an excesive load on your alternator

    if you run them flat basically you will fry the regulator and maybee even the

    rectifiers in the alternator.

    from expierience i would recomend not going beyond about 100 AH extra storage

    with a normal car/small pickup alternator.

    depending on how you set things up your alternator will only trickle charge

    your extra batteries so 1.5 hours of driving will not add a lot to your xtra batteries.

    there are ways to change the charge rate of your alternator and save your batteries and alternator etc but it takes too much technical knowledge

    to set up for most people.I dont know if there is a easy comercial setup

    to do this? honestly i have never used the rectifier based isolators and dont know if they will make the most of the charging capacity of a alternator?

    but the fact still remains that working the alternator too hard (beyond designe specs) will cause problems.designe specs for most small vehical alternators are bringing a 50 to 100 amp hour battery up to correct charge rate very quickly.(when they try to do this to a large bank they are overloaded)

    in short the alternator can put out huge amounts of energy but the regulator

    and rectifiers are probably not up to the task right out of the box.

    and then in the quest for power from an alternator you will run up against

    belt friction/slippage and finally physical bearing strength.

    in even shorter short LOL add another 10 amps to you standard alternator

    work load and you will probably be ok 10 amps for 1.5 hours is 15 AH which

    is not enough (nowhere near) to be running a fridge on a daily basis.

    does that make sense?

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