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Determine the actual mah of battery?

Discussion in 'Batteries and Chargers' started by profector, Apr 12, 2014.

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  1. profector

    profector Full Member Verified Member

    How does one determine the actual mah of a battery? I have some 18650's marked 1600, 2000, 2500, 4000, and others. I also have a few 18350's with 800, 850, and 1000. Is there a fairly simple way to test them with a multiple meter or a few items I can get from the local Radio Shack?
     
  2. derogg

    derogg Super Member ECF Veteran

    Feb 27, 2014
    Socal
    No you need a charger that tells you how many mAh are being put back into the cell. Don't think there is any other way to go about it. I'm only familiar with hobby chargers that have that capability. (I'm sure there are others too)
    - Dirk
     
  3. yo han

    yo han Super Member Verified Member ECF Veteran

    Apr 9, 2008
    the Dutch mountains
    No, the amount of milliamps charged are not accurate to determine the actual capacity of a battery. You need a charger that you can set to a certain discharge current, insert a fully charged battery and have it measure the amount of milliamps that it discharges to a certain low cutoff voltage. But like you said, almost all hobby chargers can do this.
     
  4. profector

    profector Full Member Verified Member

    So just search for "18650 hobby charger" ?
     
  5. Rickajho

    Rickajho ECF Guru Verified Member ECF Veteran

    Apr 23, 2011
    Boston MA
    Hobby charger? Yes. 18650 hobby charger? They aren't that specific. They are used largely in the RC field and are made to test all sorts of batteries, typically in packs but they can be set up to charge and test individual batteries. Like this one: IMAX B6-AC Charger/Discharger 1-6 Cells (GENUINE)
     
  6. yo han

    yo han Super Member Verified Member ECF Veteran

    Apr 9, 2008
    the Dutch mountains
    Yup, that's a good example. The name is actually quite stupid: Hobby? What kind of hobby? They should be called RC chargers or whatever. They're primarily sold to people dealing with any kind of RC models; be it planes, cars, boats or whatever that moves and runs on batteries. They're cheap, usually offer way more control than the dedicated Li-ion chargers most talked about on these forums and they let you charge at any rate, discharge, charge/discharge to storage conditions and measure battery capacity. I always wonder why it's so hard to come up with something offering the same features dedicated to cylindrical batteries...
     
  7. Rickajho

    Rickajho ECF Guru Verified Member ECF Veteran

    Apr 23, 2011
    Boston MA
    It's not that it can't be done. I have a maha MH-C9000 that's "all that" for AA & AAA NiMh cells. But the market share isn't huge for $70.00+ USD chargers. We have enough of a battle here keeping people off the "where can I get the cheapest price on a..." low end chargers as it is. They can build the same thing as a dedicated single cell Li-On diagnostic charger - if and when they ever think there is enough of a market for it. In the mean time the rather ungainly "hobby chargers" are it.

    I'm surprised that maha hasn't come out with one yet. But they seem to have gone out of their way to avoid Li-On anything to date. I would love to see what that company could come up with in Li-On chargers, diagnostic or otherwise.
     
  8. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    The problem with trying to determine the mAh of a battery is that is all depends on how fast you discharge it. Faster discharge equals less mAh. All batteries that I know of behave this way.

    Like has been discussed already, hobby chargers can help with this but they do not typically have enough discharge rate to do the 3 - 8 amp rates we typically see in vaping. Plus, we use our batteries in pulses as opposed to steady discharge. That makes a difference too. I think people who do battery graphs at various discharge rates use custom built discharge stations and data loggers to do the job. I've seen discharge rates as high as 30A graphed. If anyone has better info on how that's done, please post it, I would love to know for sure :)
     
  9. Rickajho

    Rickajho ECF Guru Verified Member ECF Veteran

    Apr 23, 2011
    Boston MA
  10. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    Thanks Rick, that's great info :thumb:! I use the lygte-info web site whenever I can for reviews, but I never thought to check if they have a how-to on the test process.
     
  11. Kemosabe

    Kemosabe Vaping Master ECF Veteran

    Sep 21, 2011
    Roe Dylin
  12. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    Here's the review on lygte-info. If you haven't seen it yet, you can look it over and see what you think Kemosabe.

    For me, I have a preference in these chargers to buy ones that do Li-ion only. IMO a Li-ion only charger will handle a problem Li-ion cell better than a charger that also does NiMH. But that's just my opinion and I'm not sure it's correct.

    The feature set is very nice. The fact that it continues to pulse power after charge is finished is a negative. I don't leave batteries on charge overnight on purpose so it rarely happens, but both my chargers shut down when charge is complete and I like it that way.

    The reviewer is I think leaning the same way in his conclusion at the bottom of the page.

    So FWIW, for me I would not buy this one. I think you can still get the Xtar WP2 for around $20 and this one is $15. The WP2 does 2 cells at a time, it's accurate and it handles Li-ion cells that have been discharged down to ridiculously low voltages. It also charges at 0.5A and 1A. That works for me, but as always YMMV.
     
  13. Kemosabe

    Kemosabe Vaping Master ECF Veteran

    Sep 21, 2011
    Roe Dylin
    i agree with you. and now that you showed the review, it reminds me that i have seen it before. i never did decide if that charger was worth its weight in salt. i must have leaned toward 'no' as i didnt buy it lol.
    the feature that tells you how many mah have been put into the battery seems handy, yet the reviewer says its not precise; might be good for comparing cells. i wonder if the xtar wp2 (or any other charger beside hobby/super-expensive) attempts to measure mah.
     
  14. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    The WP2 doesn't. It's a very basic, set the amps and go charger. I don't think any do. I check voltage drop under load when I want to see how a battery is doing. It's very easy to do with a RBA/RDA on a bottom button mechanical mod. You have to do it with the same resistance all the time for it to be an accurate indication of battery health.

    I can tell you from experience that number will increase over time. I had a couple of MNKE cells that started at about 0.4V drop at 0.6 ohms and ended up at about 1V when I retired them.
     
  15. Kemosabe

    Kemosabe Vaping Master ECF Veteran

    Sep 21, 2011
    Roe Dylin
    Wow that's quite dramatic of a swing. Good to know. So how many charge cycles do you think those mnkes received before you retired them?
     
  16. Ryedan

    Ryedan ECF Guru Verified Member ECF Veteran

    Mar 31, 2012
    Ontario, Canada
    I don't keep track of charge cycles so I have to estimate. Had them for about 1 1/2 years. For about 4 or 5 months they were the only 2 cells I had for mod use with a couple of lesser batteries tucked away as spares. The rest of the time I used 4 cells. I think they had around 200 cycles each.

    I wasn't noticing reduced vape time between charges so I could have built lower resistance coils and continued to use them for a while longer but I felt uncomfortable doing that. Batteries are cheap. I think I paid around $25 for the pair delivered so they cost me $1.39 a month. The last 14 months or so I've been vaping sub ohm on mech mods. It was worth it to me to replace them for the extra peace of mind.
     
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