# How many amps can a car battery supply?

Googling this hasn't given me much information. I've heard numbers ranging from 30A to 300A.

My question isn't how many amps a car battery does supply in normal operation, it's how many amps I would measure if a car battery is shorted across a multimeter (assuming the multimeter doesn't explode).

• Depends on the battery. – Ignacio Vazquez-Abrams Jul 14 '16 at 23:48
• Look for the "cold cranking current" rating for the battery - this won't be the maximum current the battery can deliver, but is the minimum current the battery is suposed to be able to deliver when starting a car on a cold day. – Peter Bennett Jul 14 '16 at 23:58
• In normal operation (while driving) it should supply zero or less. The alternator should be powering everything. – Mark Jul 15 '16 at 0:07
• exploding multimeter is likely outcome if it's one of the ones with the 10A range unfused. as Mr Fields says further down some thousands of amps depending on the size and condition of the battery. – Jasen Jul 15 '16 at 1:29
• Limiting current will be meter leads, internal shunt resistance and plug in connections to meter. The meter WILL blow fuse or halt and catch fire (As in \$DD in MC6800 but not resettably here). A decent hunk of copper wire - say the cable in good jumper leads terminated PROPERLY to rugged clamp on connectors and short cable length will give several times the battery CCA rating for a very short period. Car batteries usually have CCA in the 300-600A range so over 1000A possible with a solid enough cable and terminations. – Russell McMahon Jul 15 '16 at 5:05

First, it highly depends on the battery. Some cars have much beefier batteries, measured in Amp Hours. We arn't even talking about Electric Vehicle battery banks which are massive. Then it depends on the type of battery. Some chemistries are different. Some are 24V instead of 12V. Some cars have more than one. Etc.

That said, the normal peak current is the Cold Cranking Amps. This is the amount of current the battery should provide for starting a cold engine at 0°F. 300 to 1000 Amps is not unusual.

￼Finally, each battery was “dead shorted”, connected to a “shorting circuit” consisting of a shunt (5000A+ 0.25%), Hall effect transducer [model LEM LT 4000T (4000A+ 0.5%)], 26 feet of MCM-550 cable and a knife switch. A 2 channel Fluke 190 Scopemeter with automatic triggering was attached to the Hall effect transducer and to the battery terminals. Current and voltage readings were recorded at 0.2 millisecond time intervals from 0 to 0.2 seconds. An Agilent 34970 data-logger was used to monitor the shunt current and battery terminal voltage at 40 millisecond time intervals from 0 to 30 seconds. The “shorting circuit” had a resistance of 1.80 milli-ohms, as measured with a Biddle DLRO micro-ohmmeter. The inductance of the circuit was not measured.

To determine the effect of temperature, sets of UPS12-140 (12V-33AH) batteries were float charged at 13.65V (2.275 volts/cell) for 48 hours at 2, 11, 24, 33 and 40oC in a temperature-controlled environment. OCV, impedance and conductance readings were measured and each battery was “dead short” tested using the test method described above.

In theory, with a perfect conductor you are looking at over 2000 Amps. With their test, they saw 1700 Amps.

And these are just 33 Amp Hour batteries, small compared to most cars. These are UPS batteries! My car has a 150 AH battery with 750 CCA, and it's not even a premium battery.

### In short, we are talking about literal Thousands of Amps for a dead short.

But any multimeter worth a damn will have high resistance for voltage measurements, and a fuse for current measurements, that should blow before you see much current flowing. But it will blow if you short it. No if and or buts about it.

• "But it will blow if you short it. No if and or buts about it." Uh, yes, there are some ifs and buts here. Most notably, there are such things as meters designed for use on very-high-power equipment. Yes, the typical multimeter will blow way before this point, but the typical meter isn't every meter. Specialized meters do exist that will easily handle and measure very, very high currents. – Matthew Najmon Jan 28 '19 at 0:15

Hundreds of amperes. For example, my truck has a battery rated at 625 amps. Each battery should have a rating. Many auto parts stores have the ability to test the battery for you to make sure it is putting out the correct current.

• A dead short will be significantly higher than the CCA rating. – Passerby Jul 15 '16 at 0:53
• You are correct, but there is no guarantee that doing so will not cause internal damage to the battery. – Eric Urban Jul 15 '16 at 12:45
• @EricUrban That doesn't matter. Whether or not it will damage the battery is another topic for another question. This question is about how much current it will generate in whatever time it takes before the damage ends the generation of that current. – Matthew Najmon Jan 27 '19 at 23:08

Assuming the battery and the ammeter both have internal resistances of 1 milliohm, then from Ohm's law,

$$I = \frac{E}{R} = \frac{12V}{0.002\Omega} = \text {6000 amperes}$$

• This is talking about lead-acid batteries. Those tend to have rather a lot higher internal resistances than 1 milliohm. – Matthew Najmon Jan 27 '19 at 23:04

The reason you're seeing such a large range is because a battery is better thought of as a fixed voltage source, not a current source. If you have a 12V battery and you're asking how much amperage can it kick out, the answer is however much or little it has to to satisfy Ohm's law, V = IR. The less resistance you have in a circuit, the more current will flow and vice versa. The absolute extreme of this would be if you had zero resistance (an ideal short circuit), then the poor battery would try to crank out infinite current to maintain the relationship. That means kaboom.

Of course, there will always be some resistance in the real world so your battery will probably only have to try to crank out thousands of amps - still kaboom.

To answer your question: How many amps a battery supplies depends entirely on the voltage of the battery and the resistance in the circuit. It is not a fixed value for any one battery or class of batteries. Even the resistance of the circuit is not necessarily a fixed value, it would depend on factors like the level of corrosion in the terminals and the temperature of the conducting wires. If you want a ballpark of how much current your battery sometimes supplies, check the cold crank amperage rating.

• Is the internal resistance of the battery 0? – RoyC Oct 17 '17 at 8:48
• My question isn't about a theoretical ideal 12v voltage source, it's about a real car battery. If you measure the short circuit current of a AA battery, you'll get a few amps. I was asking about the short circuit current of a non-ideal car battery. – Daffy Oct 18 '17 at 21:38
• A high current draw will easily draw down the voltage of a battery. Thinking of a battery as a constant voltage source is no better than thinking of it as constant current. Batteries are not regulators. They are storage devices with internal resistance, internal capacitance, a variable SoC, and even a little bit of internal inductance. None of these things are consistent across all batteries of the same chemistry, and SoC isn't consistent with the same battery from moment to moment. All of them will alter both voltage, and the rate at which current draw pulls down voltage. – Matthew Najmon Feb 5 '18 at 19:20
• @Daffy If you measure the short-circuit current of an alkaline AA battery, you'll get a few TENS OF AMPERES. If you only see a few amps, then your multimeter's internal resistance is greatly limiting the SC current. Use a 500-amp meter, or use your test-leads alone, with no meter, and the battery SC current will be far higher. – wbeaty Mar 1 '18 at 5:10
• @wbeaty An energizer AA battery can supply a theoretical maximum of 10 amps. (150 mohms minimum at 1.5v, according to the datasheet) With the added resistance of my meter, the probes, wires, and the battery having more than the minimum resistance, it ends up being closer to 6-8 amps. That's not to say measuring the short circuit current of a battery with an unprotected meter is a good idea, but where are you getting tens of amps? – Daffy Mar 1 '18 at 22:53