My car battery gets dead if I don't use the car for 10 days or more. Is it possible to charge it using 12v 2A power supply of my dth set top box. ?

EDIT: Just measured the voltages using DMM. Car battery=12.06 V and DTH Set Top Box suppy=12.43 V.

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    Possibly, but I'd recommend you find and fix the problem, you should be able to leave a car for more than 10 days. If you can't you likely have a parasitic battery drain or a battery issue.
    – GdD
    Jan 9, 2018 at 16:53
  • @GdD added some details in question. Also whenever I ask local mechanics (about 3 of them) about this problem they replied it is normal and suggest to start engine for 15 mins every 3-4 days. I still feel that there might be some problem in car(Chevrolet Beat LT).
    – Sam Sk
    Jan 9, 2018 at 18:03
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    I believe it is best to address the problem, as others have stated. I also believe it is best to use a proper battery charger as Paulster2 suggested. If you decide to use the power supply, then keep Ohms law in mind. A resistor in series with the power supply will limit the current (assuming the power supply does not have current limit). Also keep in mind that if the battery voltage is higher than the supply voltage, current will flow into the supply. This could be very dangerous. Jan 9, 2018 at 18:13
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    @ Sam Sk. That is this time, but it may not be next time. When a power supply is loaded, the output voltage can have transient dips/peaks. It is possible that the output voltage of the power supply has a transient that goes below the car battery voltage and blows up. Car batteries are capable of delivering a LOT of power so I'd go with a proper charger with safety/protective circuitry. Jan 9, 2018 at 18:21
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    Making your own battery charger is dangerous. I would advise against it. With that being said, it is very uncommon for a battery to die within 10 days of non-use unless 1) there is a drain, 2) the ambient conditions are extreme, or 3) the battery is faulty. Without resolving the problem itself, an easy workaround would be to disconnect the battery when not in use. In cases 2 & 3, that may not even help.
    – CharlieRB
    Jan 9, 2018 at 21:56

1 Answer 1


You could do this, but you'll have an issue. The charger isn't intelligent enough to know when to stop charging. This means over time it will over charge the battery, causing it to kill the battery in the process. A typical battery charger (at least newer ones) have systems built in which will charge the battery to capacity, then check it often enough to know when it needs a little something more, but won't overcharge and damage the battery in the first place.

There are plenty of "battery tender" type charges on the market which are a much better alternative. These are relatively cheap (under $20 here in the States), and provide the battery conditioning needed to keep your battery in tip-top shape without issues. Invest a small amount of money into this and you shouldn't have to worry about a battery except when the battery is worn out.

On that note, if your battery is at or near the five year mark, consider replacing it. You may also want to check your vehicle to see if there's a constant power drain causing your battery to go bad. You should be able to leave your vehicle for much longer than 10 days and still have the battery work without issue. There may be something else going on with the vehicle which you'll need to look into if it isn't.

  • @Paulster2 Added some details in question. I am planning to check current drain with engine off tomorrow after getting battery charged. I am thinking of putting my Multimeter (in 10A mode) in series of -ve terminal of battery. How much drain current is normal when car parked? EDIT: battery is just about 15 months old Amaron make.
    – Sam Sk
    Jan 9, 2018 at 18:14
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    @SamSk mechanics.stackexchange.com/q/26651/15036
    – agentp
    Jan 9, 2018 at 19:33
  • @agentp as many of users suggested in this post against using own charging, I got it done at auto shop overnight. Now, first I connected the battery with ampere meter in series as suggested. Idle drain current found was 0.15A which gives 13.88 days life for my 50AH battery.
    – Sam Sk
    Jan 11, 2018 at 10:47
  • The voltage, 12.43 V, will certainly stop charging before the battery becomes full. In fact, it is not enough to charge a lead-acid battery. Even float charge is over 13 volts.
    – juhist
    Aug 29, 2019 at 17:48

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