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When we go out and look for phones, the first thing I do I always look at the battery capacity, usually 2000 mAh, 3000, up to 10000 mAh for a (external?) battery.

Looking at laptop batteries, they are much much larger and have only afraction of what the most massive batteries for phones have.

My laptop battery has, for example, 5000 mAh, probably not much higher than 15-20V,

if I get four 10,000 mAh phone batteries I get the same voltage range in serial connection and still those 10,000 mAh, or not? (or maybe 40,000 mAh). Yet I will save space.

Is it a wise choice to construct such a battery for my laptop?

Is my logic correct?

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Why not google "LiPo batteries for laptops"? –  Andy aka Apr 23 at 11:31
3  
One other item not mentioned in other answers is that after the "exploding laptop" debacle years ago, laptop manufacturers have been using less efficient, but safer, battery chemistries. Cellular phone manufacturers have been focusing on more efficient (watts/weight/volume) cells to decrease phone size. That being said, the latest laptops aren't that different from the latest phones. If you want to compare them, please provide the models of the phone and the laptop to compare. Otherwise all you can get is generalities such as below. –  Adam Davis Apr 23 at 17:16

4 Answers 4

up vote 22 down vote accepted

Until recently, all lithium laptop batteries were made up of cylindrical lithium-ion cells. Now, many designs are using a lithium polymer (pouch) type battery in laptops. This is allowing the thinner laptop designs.

The properties of the cylindrical and the polymer cells are almost the same. The advantage of the soft pouch construction allows the same capacity battery fit into a smaller space, due to not having air voids between the cylindrical cells.

It is also important to note that many after market phone battery capacities are pulled from a data sheet that was printed in a Fantasy Land where everyone rides unicorns.

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+1 for unicorns. Especially from some ebay or cheap chineese suppliers where they claim their ultrafire 18650 cells have 10 billion mah capacities. –  Grant Apr 23 at 13:09
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@Grant I still wouldn't buy a Lithium polymer batteries called Ultrafire. It makes me nervous thinking about that in my pocket. –  JFA Apr 23 at 20:24
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@jfa The best are the trustfire brand. You can always trust them to start a fire :) –  Grant Apr 23 at 20:39
    
I run an unprotected Ultrafire 10440 cell in my every day carry AAA LED flashlight. Partly, because they are the only ones that seem to make them. –  Joe Apr 23 at 21:46
    
You are mixing up terminology here. The non-cylindrical batteries are called prismatic. Most battery chemistries support either manufacturing process, with some restrictions, LiPo (Lithium Polymer) can be both cylindrical or prismatic. It's simply that as a newer chemistry and the trend of the industry towards prismatic, the manufacturing lines tend to be prismatic. –  placeholder Jun 23 at 3:56

You can't compare different voltage battery capacities in mAh. You have to calculate watt hour capacity (real energy).

$$Wh = Ah \cdot V$$

For 2000mAh 3.7V phone battery (example) - capacity is:

$$2000 \cdot 3.7 = 7400mWh = 7.4Wh$$

For 11.1V 2000mAh battery it will be

$$11.1 \cdot 2000 = 22200mWh = 22.2Wh$$

So energy is different, but constant current capacity are the same. When you buy battery - you pay for energy capacity, not mAh. In reasonable quality devices battery technology is the same, allows the same energy density per mass or size. Some laptop batteries have complicated circuits built in, and you typically pay more per 1 Wh.

Watch EEVblog #140 - Battery Capacity Tutorial for more information. There is an explanation why Ah unit is used more than Wh.

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+1. Your laptop (and its heavy duty screen, hard drive, ssd, many usb plugs, etc) will most probably need more Wh than your phone... so you shouldn't be able to replace one with the other, unless the replacement has enough Wh for all your use(s). –  Olivier Dulac Apr 24 at 14:54

Both batteries use the same (or comparable) battery chemistry, but the laptop battery

  1. has a much higher voltage (11.1V to 16.8V vs. 3.7V), and
  2. has both protection and charging technology built-in rather than in the main device itself.

These lead to a discrepancy in both capacity in Ah and in overall energy density, and is one of the main reasons why capacity in Wh is more accurate (since Wh describes how much energy the battery actually contains rather than how much current can be drawn from it over time).

So to answer your question, while it may be possible to construct a laptop battery from discrete components, it is almost never practical to do so, and perhaps just a little unwise.

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A genuine battery for my phone costs £10 and is 1.2Ah @ 3.7V, for my laptop £23 and 4.8Ah @ 10.8V. Making a laptop from the phone batteries would require x4 for capacity and x3 for voltage, costing £120 instead. I don't see a particular gain there.

You may be able to source cheaper batteries which claim higher capacity. If you're lucky, they may not explode.

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