0
\$\begingroup\$

I have a Lithium Ion Polymer battery (EEMB LP963450) and I am trying to determine how many cells are in it, and something is not making sense with my math.

Here's the formula I am using:

Determine the number of cells in a Lithium Battery:

  1. Battery Voltage Rating / Nominal Voltage Rating = # of cells in series
  2. Battery Capacity / Nominal Capacity = # of cells in parallel
  3. number of cells in series X # of cells in parallel = # of cells total

Here are the battery specs (at least what I have found):

  • Battery Voltage Rating = 3.7 V (uncertain)
  • Nominal Voltage Rating = 3.7 V
  • Battery Capacity = 1800 mAh (uncertain)
  • Nominal Capacity = 1800 mAh

Based on the numbers above, here's my math:

  • 3.7 / 3.7 = 1
  • 1800 / 1800 = 1
  • 1 X 1 = 1 cell

About this point, you may be bored and asking, "yeah, so, what's the problem?" (if you think I have this correct)

So here's the problem.

With only one cell, this single-cell battery has 6.67WH ((mAh)*(V)/1000 = (Wh)) which is considerably over the 2.7WH per Lithium Ion cell for unlimited travel allowed on airplanes.

But this is a small battery so I am thinking I have something incorrect.

Maybe the Battery Voltage Rating and Capacity are not correct?

Maybe I'm plugging the numbers in wrong or not converting something I should be?

So my question is,

How do you determine how many cells are in a Lithium battery?

FYI Data


From EEMB:

Dear Phil, Thanks for your inquiry. This is Donna from EEMB, glad to work with you.

For the model LP963450( 3.7V/1800mAh), it is a single cell, and your following understanding is correct.

For the battery pack, it is consisting of the cells connected in series or in parallel. If the battery stacked in series, the voltage rating will be added multiply. If the battery satcked in parallel, the capacity will be added in multiply. The following example is for your ref.

1) model LP963450-2S ( 7.4V/ 1800mAh), 2 cells in series, the voltage was added

2)model LP963450-3P ( 3.7V/ 5400mAh), 3cells in parallel, the capacity was added

3)2LP963450-3 (7.4V/5400mAh), the battery stacked with 3 cells in parallel , and then 2 battery pack in series , totally 6 cells

Hope it is clear. Any problems, please let me know. Have a nice day.


A great article on Lithium-polymer batteries: The Basics of Lithium-Polymer Batteries

\$\endgroup\$
  • \$\begingroup\$ Where did you get the 2.7Wh limit from? This document from the FAA says the limit is 100Wh. \$\endgroup\$ – brhans Jan 26 '18 at 19:22
  • \$\begingroup\$ The ecfr page you linked to says the number of cells is restricted if they're over 2.7Wh, not that they're banned. \$\endgroup\$ – brhans Jan 26 '18 at 19:24
  • \$\begingroup\$ • MAX Lithium per cell 20Wh • MAX Lithium per battery 100Wh \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 26 '18 at 19:48
  • \$\begingroup\$ Are you carrying these on as a passenger or trying to ship them as a company? The rules are different. \$\endgroup\$ – vofa Jan 26 '18 at 19:48
  • \$\begingroup\$ The focus is not on the travel, but on determining the number of cells in a lithium battery. If you're interested, I am certifying a bunch of devices for a major airline. \$\endgroup\$ – PCSailor Jan 26 '18 at 20:05
1
\$\begingroup\$

How do you determine how many cells are in a Lithium battery?
My assumption is for customer travel and the present limits are;

• MAX Lithium per cell 20Wh
• MAX Lithium per battery 100Wh

The battery in question. enter image description here

LP635940 Lithium Polymer Battery
3.7V @ 1.8Ah typ. capacity at 0.2C rate
= 6.66 Wh which is less than MAX per cell limit.

How many cells in package? Only 1.
Not because of capacity but because of construction method.

What are cells?
- discrete (separate) manufactured items.

How many items here?
1

How is it made?
Many recurring thin layers of {conductor mesh , electrolyte, insulator}.

\$\endgroup\$
  • \$\begingroup\$ Hi Tony, Thanks for the details here. Excellent work and much appreciated. I am still not clear on something though. How do you determine this line; "How many cells in package? Only 1. Not because of capacity but because of construction method." Is there some math I'm missing to determine this or am I just missing some knowledge about lithium battery design? Thanks, \$\endgroup\$ – PCSailor Jan 26 '18 at 22:36
0
\$\begingroup\$

This is a picture of a perfectly valid way to transport lithium-polymer batteries in your carry-on luggage. It will cause a bit of excitement as you go through TSA, but it is completely compliant. Each battery in this pack is 56Wh, and 6 of them went through the checkpoint without issues, including passing through customs to Canada and back to the US.

I realize it doesn't really answer your question about calculating watt-hour capacity -- you've done it correctly. It's more to illustrate that a tiny cellphone-battery-sized device won't cause you any issues at all when travelling. Just make sure you've clearly shown you understand what lithium batteries are, and you've secured the leads.

enter image description here

\$\endgroup\$
  • \$\begingroup\$ yes, thank you, but my question is not asking for travel advice. My question is how to find the number of cells in a battery. I need to determine this for a number of different battery models. Thank you though <: \$\endgroup\$ – PCSailor Jan 26 '18 at 19:40
  • \$\begingroup\$ @PCSailor: I was mostly responding to the "for air travel" part :) -- and it's a funny picture I like to share with people when I can. Watching the TSA agents go finger-to the-earpiece with the "THIS IS WHAT WE TRAINED FOR" flashing across their eyes, then the subsequent letdown, is cathartic. \$\endgroup\$ – Bryan Boettcher Jan 26 '18 at 20:14
  • \$\begingroup\$ I would like to be there for that. \$\endgroup\$ – PCSailor Jan 26 '18 at 22:17
  • \$\begingroup\$ Just because you got through doesn't mean it's legal. It may of course still be, but this doesn't prove it. \$\endgroup\$ – pipe Jan 29 '18 at 14:32
  • \$\begingroup\$ @pipe: it wasn't smuggled -- it was explicitly declared, and checked by the TSA agents. As far as I can tell, it complies with their rules and multiple agents seem to agree. It's still a hilarious thing to pull out of a bag at the bag scanner though. \$\endgroup\$ – Bryan Boettcher Jan 29 '18 at 15:59
0
\$\begingroup\$

Lithium ion polymer battery cell is always 3.7V.

For the battery pack in series, divide the total voltage by 3.7 to calculate the cells.

For the battery pack in parallel, divide the total capacity by the single cell's capacity.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.