Advice needed ? Anyone used 'AA' 1.25V NiMH batteries for 550ex and 420ex before ?

Discussion in 'Canon EOS' started by wm, Dec 24, 2004.

  1. WM


    Hi folks,

    I am a 550ex and 420ex user and have been using 'AA' 1.5V alkaline
    batteries to power them, but was wondering if using
    rechargeable 'AA' NiMH batteries (listed as 1.25V, 2500mAH), would
    be a better alternative ?

    I have few concerns and was wondering if anyone here has any
    experience with those NiMH batteries ?

    1. Would the 1.25V rating of those NiMH batteries (instead of 1.5V
    alkalines) power the speedlite properly in terms of zooming, E-TTL
    and even the other functions like 2nd curtain sync, high-speed sync,
    etc ?

    2. Why are the NiMH batts rated as 1.25V instead of the usual 1.5V
    of regular alkaline 'AA' batteries ?

    3. Do the NiMH rated at 2500mAH go longer than regular alkalines and
    what do their energy decay curve look like ? (So that I won;t have
    the batteries die on me suddenly without warning at an important
    time of a shoot !)

    Any advice would be much appreciated, and Merry Christmas !

  2. Roger G

    Roger G Roger G

    I can't answer the technical questions, but I've been using NiMH in my 550ex for a while, they work great in every way, last a long time, and will save you plenty of $. Buy 8 so you always have a spare set available.
  3. I cannot comment on using standard AA 1.5V batteries, because I have ALWAYS used 1.25V NiMH batteries. :)

    You may get slightly lower battery life than with standard AA's. . .but you can't recharge standard AA's. . . .
  4. Even though alkaline batteries are rated at a nominal 1.5 volts, they only deliver 1.5 volts when they are fully charged. As they begin to discharge the voltage of alkaline batteries continuously drops. In fact, over the course of their discharge, alkaline batteries actually average about 1.2 volts. That's very close to the 1.2 volts of a NiMH battery. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volts. NiMH batteries stay at about 1.2 volts for most of their discharge cycle.

    You'll actually get higher current out of NiMH or NiCads because of lower battery internal resistance. A fairly simple application of Ohm's law can make a good approximation.

    I[current] = V[battery voltage] / (Ri[battery resistance] + Rl[load])

    For a 50 milliohm load. You'd get 16.2 amps with a charged NiMH AA, and 9.0 amps with a fresh AA alkaline. The voltage delivered to the device would be .81V with the NiMH and .45V with the alkaline. As the internal resistance increases as the battery is drained, the NiMH would still be usable when the alkaline wouldn't be able to deliver enough voltage to power the device.

    NiMH cells will generally allow flash units to recycle faster because of their low cell impedance. The characteristic voltage difference does not properly account for high-current pulsed load conditions in which the rechargeable cells will show considerably higher terminal voltage than alkalines under load.

    Decay is a bit more abrupt to alkaline batteries : it won't suddendly die on you, but once you begin to notice longer recharge times it is time to think about swapping batteries.

    One major drawback of NiMh is the low shelf life : stored at 20? C NiMH batteries will lose up to 40% of their charge within a month. If they are stored at a higher temperature, they will self discharge at an even higher rate. Make sure you charge them not too soon before using them.

    All in all, I changed to NiMh for my 380EX and I am not looking back : lower cost, shorter recharge time and longer autonomy make it a win accross the board.
  5. Hi Wee-Ming,
    NiMH batteries work WAY better than alkalines. Even my 1700mAh ones work a lot longer so, you will be even better off with the 2500mAh.
    What I do is that I use NiMH, but always have alkalines in my bag if I travel as NiMHs discharge after a while during storage. Very slowly however, but with the alkalines (no discharge when not used) I always have 100% power at hand even if there is no access to recharge, therefore no surprises. Of course, when I have access to recharge, I recharge NiMHs and don't use alkalines.
    Merry Xmas,
  6. Here's a good place to buy high quality NiMH batteries and chargers:
  7. use the indicated above, overall MUCH better than alks. The "notice" of death is much longer recycle if it starts out at say 4 seconds (just a number, forget reality right now), when it hits 3 times that I usually pull them out and pop in the back up. Dont know how much longer they would last, but the recharge time times 3 is my limit of endurance ;o)

    regarding the drain charactersistics sitting there doing nothing, that is easily resolved by just charging the 4 (that will go in flash straight away) and 4 back-ups (at least) the day before you plan on doing a major session with them.
  8. i forget the science and put nimh batteries in my 550 and they work a treat
  9. I've used NiCads in my camera and flash for close to 20 years now. Over those years I have probably only bought a total of 20 batteries and each unit takes 4.

    The one thing I have noticed is that somehow the circuitry becomes accustomed to the NiCad current because in emergencies when I have had to substitute fresh alkalines the camera only functions for a few shots, if that, and doesn't even register on the battery check gauge, and the flash although faster to recharge initially, becomes tempermental with only a few flahes. With NiCads they both run superbly.
  10. Listen to Jean-Marc. He's got your answer.

    And from a practical point of view NiMH batteries charge my 420ex faster than alkalines.
    1. The flash will work properly. If you look in the manual for the 420EX, it lists NiMH as an acceptable battery type, and I suspect the 550EX' manual says the same. NiMH also worked fine in my 380EX, even though it didn't list NiMH. In general, any device which can be powered by NiCd can also be powered by NiMH (though you can't recharge NiMH in a NiCd-only charger).
    2. Because that's their voltage. The voltage is a property of the chemical reaction that takes place in the battery, and not all chemical reactions generate exactly the same voltage.
    3. I haven't tested how many flashes I can get from a set of batteries before they die. The manual for the 420EX says that alkalines last much longer than NiCd, and I suspect alkalines last longer than NiMH, too. But the alkalines become a waste product when they run out of charge; the rechargeables go back into the charger and can be used over and over and over again. If you're worried about batteries dying mid-shoot, get two sets of batteries, and when the first set dies, pop the second set in the flash and the first set back in the charger. Or keep a set of Li batteries handy as a backup; they have a ten-year shelf life and provide faster cycle times than alkalines.
  11. I usually purchase 24 batteries before going on a shot where I need flash. Earlier this year I purchased 2000mA batteries and went through two sets when I thought I'd use triple that. I hace since replaced them with 2400mA and am amazed at the length of time they last. I was going to buy a Quantum 2x2 for more power but that may be unnecessary after all.
  12. I second what Bill said.<br>
    I only use NiMH batteries, including EOS-3 and 550EX<br>
    I think it's even better than Alkaline (not sure, but..).<br>
    Just like what Bill said, visit Thomas Distributing.<br>
    Look at Powerex batteries, they are the best.<br>
    You will find the link to an *Independent* battery test result.<br>
    You will find out that not all the NiMH batteries are the same.<br>
    One more thing, (money saving tip).<br>
    Thomas Distributing is also selling their batteries on ebay.<br>
    I think buying from ebay would save you a buck or two (after shipping).<br>
    Sorry I don't have answers to #2, #3, but Don't worry about it. Really. You'll love it.<br>
    When I do weddings, I put a fresh set in my 550EX for "before the wedding" shots.<br>
    Right before the ceremony, I put in a fresh set (even though I have plenty of juice).<br>
    And I put in a fresh set right before the B&G makes the entrance to the reception (again, I still have plenty of juice).<br>
    I honestly believe that I can do the whole wedding with just one or two sets of NiMH batteries.<br>
    But I always carry 5 sets.<br>
    Thomas distribution also gives you free battery holders, very handy.
  13. I use those NiMH in my old olympus flash, worked wonders ! always better than standard disposable batteries.
  14. I may have missed it, but I wanted to mention that with the NiMH battery, you a lower internal resistance. That translates to a faster recharge times between flashes.

    So, with the rechargeable batteries, the flash is ready faster after taking a shot.
  15. Wee ming, I`ve been using the plain blue ones from `Battery world` they were AUD5 each 2 sets are still going strong after 18mths, and the flashes are going longer and better best of all can charge at any time without memory fears

    good luck
  16. WM


    Wow ! Thanks for all the great advice ! You folks are the best ! And especially to Jean-Marc for his highly technical but elegant explanation (of which I miraculously understand !) Thanks !

    So, the net result is NiMH is the best way to go, do a full recharge the day before a big shoot, keep a set of regular lithiums in the bag (just-in-case), if the flash recharge times slow down to about 3x longer than full charge it's time to change to a new set.......and have fun !

    And also thanks again even for advice on where to buy them.
    I appreciate all your help, and Happy New Year !

    Now to do some battery shopping...........


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