Li-ion batteries from china, just how inflated are the numbers?



So, I'm working on converting a pickup truck to electric, part of the process is assembling a battery pack. Unless a person is building 1000+ electric vehicles, its hard to get a good price on anything EV related, so here is an interseting take...
Instead of buying one battery that would run the whole truck, I'm looking at buying 500+ batteries and building my own pack, this way I qualify for volume discounts.  This is NOT crazy because the time I put into it is FREE, I cant work 24 hours a day.
So I set out on two sites, ebay and alibaba express, to see what the 'best' price on batteries was and how much it would cost to put togethor a pack.
Now dont get me wrong here, I'm not buying the cheapest stuff off ebay and expecting it to give me full performance, so I'm getting a few samples and testing them out to see what I do get.

My pack design goal is ~600V, ~100A (or a configuration of that number of cells)
...should be about 12kWh or more, I won't get into the truck specs.

Here is the test of my first sample. This particular listing is for a really common lithium ion battery, I can get almost identicle cells from alibaba express for just a little over $1 ea.

I would like to point out that I do not hold anything against the SELLERS of these products

http://www.ebay.ca/itm/370812730210
(we shall see how long the listing stays up)
(ya, ya, Ultra Fire, your snickering for the same reason I did)

The specs are:
  • UF 18650 rechargeable li-ion lithium battery.
  • Over charge and discharge protection.
  • Rechargeable times: Up to 500 times.
  • Capacity: 4900mAh.
  • Voltage: 3.7V.

    • Now, this concerns me, primarily because, if this battery has a protection circuit, and I have a 600V array, and it tries to open the circuit,  its probably gonna cause a really quick, instant fire. Also, caught my eye, was 500 cycle life... !?!?! thats a red alarm about something.... (tho 500 cycles would be about 4-5 years in my truck)

    ~22days later my cells arrive (acutally, iirc, they arrived much faster)

    I wanted to be really fair to these batteries, give them as much chance to pass a test as possable.

    Step one is to charge them, here is my charger and improvised battery... holder.
    My charger is  http://eds.dyndns.org/~ircjunk/circuits/lionchg3.pdf
    I noticed something odd playing with the charger, no automatic cutout behaviour, which I'd expected getting around the 4.2V mark, ok...



    I built a constant current load for them, put a voltage divider on it to step the voltage down for an AVR to send data off to a logging computer for me.
    Here I'v used one of my generic AVR baords, I have my generic IO firmware on it, which I'm using to read the battery votlage, and operate a cutout relay.
    http://eds.dyndns.org/~ircjunk/avr/babyboard_mk3/babyboard_III.html
    http://eds.dyndns.org/~ircjunk/programming/c/ioman/

    The current regulator is the basic 'fet boosted' op-amp regulated current source.



    This battery is marked 4.9Ah, which is probably the 20hr rate, so, the 20hr current would be 5/20 (ooo I rounded) = 250mA ok.
    With the constant current circuit set to 250mA, I began logging, here is my data.

    FILE_HERE

    and charting (I html-crunched the image, view-image to see fullscale)



    So, at 250mA, it hit cutoff (I'm calling it at 3V) in about 13800 seconds (3.8 hours)
    from curiosity, I calculated the Wh, which comes out to about 1.6Wh

    A VERRY hard chart to find on the internet is the voltage-time chart for various battery capacities, these only seem to be available for lead acid, which have slightly evil curves at high currents...
    This great pdf has one of these charts...
    http://www.batteryweb.com/manuals/techman.pdf
    on page 6.

    According to this chart, at 0.25A, lasting 3.8 hours, the battery lands almost exactly on the 1.3Ah curve.

    so, ok, 1.3Ah, a bit different than the 4.9Ah marked on the battery.
    so, as it turns out, this cell form comes in capacities of up to 3.4Ah, so, 4.9Ah really is out to lunch. (  http://en.wikipedia.org/wiki/List_of_battery_sizes )
    And another thing, no cutoff! (maybe I just didn't hit it?)

    Next I recharged the cell, the top 0.2V took a LONG time to finish.... (but no heat!)
    I got a spare battery for the express intention of opening it (I want to see the PCB they fit in here)

    Please dont think this is safe...

    Step A, lose the label...
    At this point, I really expected to see a plastic tube with a battery in one end and a pcb on the other, but its a sealed metal tube, ok, maybe the PCB is in a coin form on the end inside...

    Step B, removal of funny plastic washer...
    there is a small plastic washer on the end, so I started to carefully pry that off with an xacto knife... and I briefly shorted the cell, which darn near burned the tip off the knife.. "short circuit protection" so I prolly just fried the PCB right?, wrong... its still alive.... hmmm
    This reveals nothing, this thing was formed into one peice during manufacture, damn...

    Step C, cut the top off.
    Now, I should mention that this is not the first battery I'v ever taken apart in my life, I know that, on the anode side, there is USUALLY an air gap, trying to hit that gap I took my TRUSTY dremel KNOCKOFF to Carefully cut the end off. While doing this with a fully recharged (why did I go and recharge it anyhow)
    While cutting (staying as shallow as I could) clear gel was comming out, a bit concerning... (maybe its just protection gel for that pcb?)

    Within was a set of rolled plates, (uh, PCB must be in the bottom then, right?)

    Step D, pulling out the guts
    I was easily able to slide the roll out of the case, looked a bit crude, but ok.
    Looking down into the case, I see no PCB... WELL THIS IS CLEVER, it must be in the core of the plate roll then... right?



    Step E, unrolling
    ok, I really can't stress how dangerous it is to have half a charged li-ion battery unrolled, with the plates exposed AND trying to each roll up into their favorite form.
    but no inncodents. The battery came apart much the same as you would expect for a capacitor.
    Now all apart on the table, I starred really carefully, NO PCB! not even an inline fuse! THIS IS A RAW CELL!
    (to my understanding raw cells are illegal in N.A. because people are doo dumb and hurt themselfs with them)
    But this is cool for making a truck pack where I dont want a protection circuit in there.










    HUH.

    ok, well, in the process of that I assembled the hardware to test battery capacity to a silly degree, and obtained 3 (remaining) 1.3(ish)Ah li-ion batteries, $2 ea, I'm not dis-satisfied.

    I found something to compare to as well!
    This fellow has done a lot of great testing work.
    http://lygte-info.dk/review/batteries2012/UltraFire%20BRC18650%203000mAh%20%28Red-silver%29%20UK.html

    no good for my EV truck tho...

    Its not possable to say for sure, but maybe they rated the battery capacity backwards from the maximum discharge current?

    I look forward to comments!