XPS 15 Customization

[btm710]

Hey guys, looking at the Dell XPS 15 and I want to know more about the internal customization.  I've heard on reviews that the model that comes with the 84Wh battery specifically does not come with a 2.5" HDD.  Can anyone tell me if this is due to a larger battery size or some physical reason?  I don't plan on getting the highest end model but I do want the bigger battery.  Also, I see that it has a PCIe M.2 slot.  Does anyone know what revision of PCIe this supports?  I assume 3 but I'd like to be sure.

[Enderman]

yes larger capacity batteries use more space

you cant magically make a battery store more energy by throwing money at it

[btm710]

12 minutes ago, Enderman said:

yes larger capacity batteries use more space

you cant magically make a battery store more energy by throwing money at it

I mean, you totally can.  More expensive batteries could have higher energy density.  In this case it looks like the opposite is true.  The 56Wh is 3 cells and the 84Wh is 6 cells.  Math says they're not proportional.

[Enderman]

6 minutes ago, btm710 said:

I mean, you totally can.  More expensive batteries could have higher energy density.  In this case it looks like the opposite is true.  The 56Wh is 3 cells and the 84Wh is 6 cells.  Math says they're not proportional.

uh, what?

i dont think you understand how batteries work

 

3 cell = 11.1v

56/11.1 = 5 Ah each

 

6 cell = 3s2p

84/11.1 = 7.6 / 2 = 3.8 Ah each

 

3.8Ah batteries are smaller than 5Ah batteries

you cannot compare cells  "oh six is twice as large as three" thats not how it works

 

three 5Ah batteries take up less space than six 3.8 Ah batteries

[Squirrel724]

24 minutes ago, btm710 said:

I mean, you totally can.  More expensive batteries could have higher energy density.  In this case it looks like the opposite is true.  The 56Wh is 3 cells and the 84Wh is 6 cells.  Math says they're not proportional.

Not all the cells are the same size. The capacity of the cell is determined by the chemical makeup of the cell and the physical size of the cell. You can have larger or smaller lithium cells that will in turn give you more or less capacity. The 84Wh uses 6 cells that are smaller, and thus have a lower capacity per cell, then the 3 cells used in the 56Wh pack. The 3 cell pack allows for a 2.5in drive to be placed on the right side of the laptop, while the 84Wh pack is the entire width of the laptop. The laptop needs 11.4v to operate and lithium cells produce 3.8v per cell. In the 3 cell pack all the cells are wired in series to produce the necessary voltage. The 6 cell pack uses 2 sets of 3 cells in series (for the voltage) which are wired in parallel for the capacity. 6 smaller cells are used instead of 3 larger cells as it is more cost effective to produce more smaller cells than fewer larger cells.

Here is the 56Wh xps 15, you can see the 3 individual cells in the pack as well as the 2.5in drive bay:

And this is the 84Wh xps 15, you can see the 6 individual cells (you have to look kinda close) and the lack of a drive bay:

Yes you could theoretically make a 84Wh pack that would occupy the same space as the 56Wh pack however it would probably cost at least 5x as much to produce as the pack that was used (you would be looking at a $1000 battery).