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I'm gonna install a camera system in my car and it takes 12v/2a. (12v/1a times 2... it has 2 devices that run 1a each)

How long would that take to drain the battery if the car is powered off?

I was thinking about getting a small battery and running it off that then when the car starts it just pulls power from the cigarette lighter to charge the small battery but I'm not too sure how I could do that.

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It depends on your battery.

A standard car battery is about 50 Ah (Amp hours) which will supply 2 Amps for about 25 hours, or just over a day. The battery will fail to start the car well before the estimated 50 Ah mark.

Look up the rating of your battery, and divide it by 2 A to get the number of hours you can run the cameras.

Ah/A = h

I'm guessing that the 2 Amp draw is the maximum rated draw of the cameras, so actual draw will probably be less, and the battery will probably last longer, but that is something you'll need to determine experimentally.

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  • I'd have to disagree with your assessment somewhat. A 50Ah battery can maintain the 2A power draw for 25 hours, yes, but somewhere along the line it won't have enough juice to start the engine. I don't know how many amps a starter would draw, but I'll guarantee you after a certain amount of time well before 25 hours has past, you'll no longer have enough energy to start the vehicle.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jun 14, 2019 at 22:11
  • @Pᴀᴜʟsᴛᴇʀ2, I didn't mean to imply that the car would start up to but not including 25 hours. I merely wanted to point out that draining the battery has negative consequences.
    – the_storyteller
    Commented Jun 14, 2019 at 22:16
  • I get that, however, the gist of the question is, How long can I run the cameras until I can't start the car? ... or something to that effect. I was just pointing out there will be negative consequences well before the battery is drained. The way your answer reads, the OP should be good up until 25 hours, which would not be so.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jun 15, 2019 at 1:44
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There are devices specifically designed to allow one to power components from the battery with the key off. In the case of the unit I have, it runs a dash camera until the vehicle battery reaches a specified (and adjustable) low voltage. This ensures the ability to start a healthy vehicle, although it will power off the component being operated at that time.

One such item is the Vico Power Plus discharge prevention device, although this link shows currently unavailable.

It may provide enough information to enable you to locate a similar or suitable replacement.

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