Instructables

How many Ah are car batteries?

I want to know how many Amp hours a car battery has? I need to know how long I can use them for particular things.
Also how many Amps will you be able to draw from a moderate sized one? I need to know how much I can squeeze out of them before I start experimenting with them.

what ended up being the answer?

Hour many hours can a battery pull 1 amp?

Is it better to buy a 120ah deep cycle battery for your car, if it runs accessories?

A deep-cycle battery has an acid only extra inches below the lead plates. This arrangement lets flakes off of the lead sulfate plates collect on the bottom for a longer time due to charge / discharge cycling before the lead scrap heap shorts the cell plates and stops battery action.

A 120ah ( amp-hour ) battery can deliver 1 amp for 120 hrs OR 2 amps for 60 hrs OR 3 amps for 40 hrs OR 4 amps for 30 hrs OR 6 amps for under 20 hrs OR 12 amps for under 9 hrs...........

A 24ah battery can deliver 1 amp for about 24 hrs, OR 2 amps for 12 hours , etc

Lead acid 12 volt car batteries are fully discharged around 8 volts and if they are discharged below 6 volts they may not hold a charge reliably.

What is your accessories current load ?

Are you running your accessories with the engine running or just batteries ?

iceng3 years ago
Back when I worked 8 to 5 we compared lead acid battery about 13 watt hrs per pound of battery and 1300 watt hrs a pound of gasoline if my memory serves.
I would suggest checking the manufacturer website for this info because batteries are VERY different from one brand to another. On top of that there are different kinds of batteries. Marine batteries, also known as deep-cycle batteries, are made to be used without constant recharge. This means you can go spend the day on the boat all day then take it home and charge back up overnight, whereas a "standard" battery is not made to run for long on its own. Example? When your car's alternator died while driving how far did you get? Not very far.
This doesn't answer your question, but hopefully it is helpful.
lemonie3 years ago

You can easily get 60Ah, and 60A - they're pretty good, but have a good charger.

L
Vyger3 years ago
It also varies with the temperature. That is why in the winter you have a harder time starting, not only is the engine stiffer but the battery is putting out less power. In really cold climates they even use electric battery warmers to try and keep the output up. Cold Cranking Amps does not refer to the engine being cold but rather to the output of the battery at lower temps.
rickharris3 years ago
This will give you some idea of the spread. Capacity and physical size are of course connected. 

http://www.rapidonline.com/Electrical-Power/Batteries/Lead-Acid/TruPower-Sealed-lead-acid-batteries-SLA/178141


SSA, Short circuit amps, for a lead acid battery can easily top 1000A.
However, you can only pull that for a few seconds- long enough to fuse a wrench across the terminals.

The actual energy capacity is surprisingly small - 80Ah is pretty typical.
Steve
The MadScientist (author)  steveastrouk3 years ago
I thought it would be more like 40Ah but I wasn't sure.
Depends, diesels are often quite grunty batteries.

Steve
That depends on the battery.

If you want to know how much juice the battery has, a google search , a search through the manufacturers website, or a search through distributors sites, or even a call to the manufacturer/distributors with the product number/ID will usually yield a MSDS or some sort of specifications sheet of that particular battery which should tell you 1) the batteries chemistry, 2) the voltage, and 3) the Ah capacity, better sheets will also give you graphs of various aspects of the battery.

As for how much current you can draw, in a perfect system (eg there is no resistance except for the load) you could draw an infinite number of amps, but IRL the battery has an internal resistance, your wiring puts limitations on energy capacity, and a host of other reasons. you could pull an incredible amount of current, but due to the Ah capacity of the battery, you can sustain that current for only a short period. Basically, the current you can pull is only limited by the load (its why LED circuits usually have resistors).