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Bench Test Results: Eizfan 40A 2500mAh 18650...hugely overrated, appears to be Samsung 25R

Discussion in 'Batteries and Chargers' started by Mooch, Dec 4, 2018.

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  1. Mooch

    Mooch Electron Wrangler Verified Member ECF Veteran

    Supporting member
    May 13, 2015
    These tests below only note the ESTIMATED ratings for these batteries at the time I tested them. Any battery that is not a genuine Samsung, Sony, Murata, LG, Panasonic, Molicel, or Sanyo can change at any time! This is one of the hazards of using “rewrapped” or batteries from other manufacturers so carefully research any battery you are considering using before purchasing.

    Misusing or mishandling lithium-ion batteries can pose a SERIOUS RISK of personal injury or property damage. Use of these batteries is AT YOUR OWN RISK. They are not meant to be used outside of a protected battery pack. Never exceed the battery’s current rating and keep the plastic wrap and top insulating ring in perfect condition.

    Testing batteries at their limits is dangerous and should never, ever, be attempted by anyone who has not thoroughly studied the dangers involved, understands the risks, has the proper equipment, and takes all appropriate safety precautions.

    If the battery has only one current rating number, or if it only says "max", then I have to assume the battery is rated at that current level for any type of discharge, including continuous.

    2F4EDA41-D1A5-4880-A852-E86F5929F104.jpeg 3EF5FEA7-9251-4C51-9D5C-8E9FF8FC16C4.jpeg DD054009-2810-4400-B725-F194AB348B52.jpeg A751C908-8B3E-42FF-9677-72F82A189AA8.jpeg C2D17FD5-461E-456D-BEDC-E7874A864266.jpeg


    Bottom Line
    This cell just has a 40A “max” rating on the wrap but looks and performs identically to the Samsung 25R, a cell rated at 20A. To add to the confusion, Efan’s Alibaba web page seems to list this as a 35A continuous cell.

    Efan says that they are rewrapping this cell, giving it a 25A continuous rating and a 40A “max” rating. But 25A continuous is also an exaggerated rating as it heats the cell to over 90°C. That is too high a temperature to allow for decent cycle life.

    The datasheet says the 40A rating is a “Max Short Time Discharging Current” rating. Efan says this time is a “few seconds” but the rating is useless without knowing the length of the pulse, the time between pulses, and the criteria used to set the rating (temperature? voltage sag? cycle life? A combination of those?). I was unable to get Efan to give me this information.

    Efan denies that this is a rewrap but I examined the cell with a loupe, even looking at the bend radii and metal thicknesses of the top contact structure and the tooling marks on the cell, and this Eizfan is identical to the 25R. It performs the same and is also the same size and weight as the 25R.

    Something I don’t talk about nearly enough...the incorrect use of “IMR” on so many rewrapped cells. This Eizfan does not use the LMO (lithium-manganese-oxide) battery chemistry associated with the “IMR” model number prefix. The Samsung 25R uses NCA chemistry (nickel-cobalt-aluminum).

    The capacity for two of the four cells I tested was 2568mAh and 2572mAh. This is fantastic consistency and typical of cells from the large OEM manufacturers like Samsung, Sony, etc. China manufactured cells usually have much worse cell-to-cell consistency.

    I am giving this cell ratings of 20A and 2500mAh.

    Four cells were donated for the purposes of testing by Efan (Shenzhen Yi Fang Technology Co., Ltd. - IMR Battery, Li-Ion Battery). Thank you!


    Continuous Current Discharge Graphs
    C9164D65-700D-4504-9847-94755604D2F9.jpeg F185988B-91C6-4A22-AF10-6505716C2D46.jpeg


    Ratings Graphic
    15FD5ADE-03AC-459F-BC85-2E5C490D1503.jpeg


    Performance Specs
    DC Internal Resistance = 20.3mOhms (milliohms) average for two cells.
    Total energy delivered down to 3.2V at 10A continuous = 6.9Wh
    Total energy delivered down to 3.2V at 20A continuous = 4.8Wh

    I want to work for the vaping community full time! If you feel what I do is worth a couple dollars a month and you would like early access to battery availability and testing news and a say in what I test then please consider becoming a patron and supporting my testing efforts: Battery Mooch is creating battery tests and educating vapers | Patreon.

    Efan paid a fee to be moved to the front of the testing queue, which currently has a 10-12 week backlog. This cannot influence my test results as this is science, resulting in hard data, not a subjective review. In addition, they pay in advance, have no say about what is in this report, and I don’t care if any company never does this or donates batteries again. My reputation is a lot more important than any battery donation or fee to be moved to the front of the queue.

    To see how other cells have tested check out this link: List of Battery Tests | E-Cigarette Forum
     
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