Why are laptop batterys so weak for their size compared to other electronics

Factual Questions
1

I’ve been reading up on batteries, and apparently my laptop (which is relatively new) has about a 5000mah battery.

I’ve seen extended batteries for cell phones that are 3500mah. The ipad 3 has a 11666 mah battery.

http://www.amazon.com/Samsung-Fascinate-SCH-I500-Mesmerize-Extended/dp/B005AV5WO8/ref=sr_1_2?ie=UTF8&qid=1358644358&sr=8-2&keywords=extended+cell+phone+battery

Why would a laptop battery, which is so much bigger than a cell phone battery, only have 50% more capacity than that cell phone battery above?

Aren’t all batteries lithium-ion?

http://www.amazon.com/New-Trent-IMP52D-Thunderbolt-Blackberry/dp/B0013G8PTS/ref=pd_cp_pc_1

That tiny thing which is only about 4.6 ounces is about the same mah capacity as my laptop battery which is much bigger.

2

Because, mAH, doesn’t mean anything.
Or, rather, it only means something when comparing batteries of the same voltage.

My MacBook has a 55 Watt-hour battery in it. Compare that to the iPhone, which has a 5.2 WH battery.

So, Laptop batteries are much higher voltage, which gives them much more power.

3

As beowulff said, mAH doesn’t tell you how much energy the battery can store. It tells you how much current it can supply and for how long - but power is current*voltage (measured in watt). And the amount of energy stored is measured by watt-hours.

A rechargeable AA battery with 2000 mAh capacity has only 1.2 V voltage, so it only stores 2.4 WH of energy. The battery inside the iPhone 5 is 1434 mAh at 3.8V, which is 5.45 WH. The extended battery you linked to is 3500 mAh at 3.8V, so that’s 13.3 WH. I don’t know what voltage your 5000 mAh laptop battery is, but 10.8V is pretty common, which would put it at 54.0 WH capacity. If it’s 14.8V (also common), it can store 74 WH of energy.

4

Why the hell are we measuring energy in WH and not KJ?

5

Because it’s much easier to use when dealing with volts and amperes, as we usually do in electronics.

6

The short answer is that laptops are drastically higher in power consumption than say… a cell phone, camera or other portable electronics.

So even using the same battery technology, the laptop batteries are larger, and run out faster.

It’s almost like asking why a Cadillac gets so much worse fuel economy than a Vespa- don’t they both run on gasoline internal combustion engines?

7

This is the perfect “Microsoft tech support” answer - factually correct, but completely useless with respect to the original question.

8

Another thing to take into account is that the same battery will have a different mAh rating for different discharge currents.

Here is the datasheet for a 9v Energizer battery: http://data.energizer.com/PDFs/522.pdf

The mAh rating is as high as 600mAh at 25mA discharge current and drops to 300mAh for a 500mA discharge current.