# Light bar vs Car battery

I have a light bar that pulls close to 22 amps how long can I have it on and my jeep off without hurting my battery?

• It depends on how powerful your battery is. Perhaps if you list the model of battery someone can figure it out for you. There are many different types of 12volt battery from compact car to full sized pickup. All have different amperage and storage characteristics based upon their intended use. Jun 3 '16 at 7:32

Calculate it yourself:

If you have a full 66Ah battery, it will be drained within 66Ah/22A=3h.

BUT:

• A battery degrades over time, after a few years, the capacity isn't 66Ah any more.
• An almost empty battery isn't capable to deliver the same max. current as a full battery. If it's almost empty, you could have problems staring your motor. This is even more important in cold conditions.
• It takes quite a while for the car to charge a fully discharged battery. May be an hour or two?
• Deeply discharging a battery damages it. A 12V is considered empty when it gives about 11.5V. But you can still draw current, which will then damage the battery and reduce it's full capacity.

I'd say depending on the age and condition of the battery, when math says 3h, don't use it for more than 2h, better less. You never REALLY know how much capacity your battery has, and how full it is.

BTW: 22A*12V=264W. Are you lighting a sports field? Maybe, LEDs are an alternative?

• Great answer! +1! If I could add two things; the reason the battery starts being damaged is due to sulfation or sulfur crystals start growing on the plates. This makes it so electrons don't flow through these areas and the battery is depreciated. Secondly, if it is important to have the ability to run a light bar without the engine running, consider installing a second battery which is decoupled from the first. When the engine is off, it only draws from the second battery, which can be a deep cycle, leaving your main one unharmed. Jun 3 '16 at 11:09
• I doubt the light bar is actually drawing 22A. If it's an LED lightbar, they often list their wattage equivalence to incadescent rather than their actual draw. Jun 29 '16 at 0:32
• @PaulDufresne: That's quite possible. May be it's 22 W, which then is or is not an equivalent? Who knows. As I wrote, 22A means 264W, which is really really much. Jun 29 '16 at 7:16