Canon advisory re speedlights and lithium AA batteries

<p><a href="http://bit.ly/1wrQj0T">Canon advisory re speedlights and lithium AA batteries</a></p>

<p>Henry Posner<br /><strong>B&H Photo-Video</strong></p>

<p>Who am I to argue with Canon, but I have been using lithium batteries manufactured by the drum playing rodent for about two years now without a problem in my 580II.<br>

<br /> -Dave</p>

<p>Henry,</p>

<p>Thanks for posting this. I have been using Ansmann and Powerex NiMH batteries (purchased from your store, by the way) in mine, with good results, but it is good to know for the future that lithium batteries pose a risk.</p>

<p>Dave--they are not saying it will always happen; they specifically say that it will happen <em>in rare cases</em> with some batteries. That's enough for me to avoid them. I buy fire insurance even though the odds of a house fire are very low. However, others may want to take the small risk.</p>

<p>Dan</p>

<p>I suspect the problem might happen with long sequences of rapid flash bursts. The Li cells can supply a lot of current and can recharge the flash quickly. The speedlites are not really designed for many, many full power flashes in a short time. They will overheat. In that case I think they should shut themselves down until they cool, but I guess maybe sometimes that protection doesn't work as well as it should.</p>

<p>It may be that to be on the safe side, Canon simply advise against their use.</p>

<p>It's also possible that badly designed or manufactured (i.e. dirt cheap) Li AA batteries could develop internal shorts leading to high current discharge and overheating.</p>

The good news is that it only applies for residents of the U.S. and Puerto Rico, then it won't affect my flashes because I

don't live there, even while I buy my gear from B&H. Obviously kidding, but it's ridiculous how this kind of message gets

such a footnote.

 

Anyway, thanks for the info.

<p>I used Everready lithium AA's in an auto-thyristor flash once several years ago. After a few normal usages a capacitor emitted a loud pop and a puff of smoke. Funny thing, that flash unit continued to work fine for a few more years.</p>

<p>Later I tried lithium AA's in P&S digicams. They didn't last any longer than good quality alkaline AA's, which is to say, they only lasted for maybe a dozen shots.</p>

<p>I stopped using lithium AA's in anything other than flashlights. Too expensive for anything else.</p>

<p>I can't see why it shouldn't apply to the Speedlite 90EX as well.<br>

Not that I use lithium primary cells; far too expensive.</p>

<p>Henry</p>

<p><em>The Li cells can supply a lot of current and can recharge the flash quickly.</em></p>

<p>Are you sure this is the case? In Nikon speedlights, Lithium AA batteries give a relatively <em>slow</em> recharge time of about 4.5s (SB-910), but the batteries are very light weight and hold a lot of charge, so you can get many full-energy flashes and they hold the charge for a long time. For this reason I pack in lithium batteries to use as backup at events. Using rechargeable NiMH batteries, the recycle time is about 2.3s and AA alkalines 4.0s. It is possible that Nikon deliberately limits the current to prevent overheating, but in practical use these batteries have the drawback of slow recycling in Nikon flashes. I have never experienced overheating with them. I use NiMH (Sanyo Eneloop) batteries as primary power source in speedlights for the much faster recycle time. Canon flashes may obviously be different in the recharge behaviour vs. battery type.</p>

<p>To avoid the potential problem, just use rechargeable NiMH batteries.</p>

<p>I have used Lithium AA batteries in my Nikon SB-800 flash, and it turns out that they provide very slow flash recycle time, as specified in the flash manual (which of course I didn't read thoroughly beforehand). After checking the manual, I started using rechargeable NiMH AA batteries in the flashes instead.</p>

<p>I used to use Lithium AA in my film SLRs (Nikon F5 and F100). Lithium AAs last longer and are lighter in weight than alkaline AA. (The F5 takes 8 AA batteries, and the weight adds up.) Lithium handles the cold climate such as the Arctic and Antarctica much better. They provide a more constant current but have a rapid drop off at the very end. When I was using Lithium AA in film SLRs, suddenly they would drop dead with little warning. Alkalines usually slow down towards the end, and you maybe able to squeeze out another roll or two of film or at least a number of frames.</p>

<p>Typically a Li ion battery has an internal resistance (max current capacity) that's between that of a NiCd and an NiMH AA battery. But that's Li-ion. The AAs are Li - Iron Disulphide and the chemistry is a bit different. They have a higher voltage than either NiCd or NiMH. Though they are nominally 1.5v, off load they typically measure 1.6 or 1.7 volts.</p>

<p>The original Energizer Li AA cells were limited to 1.5A discharge current (2A for pulses), but the newer "Ultimate" energizer Li AA cells are rated for 3A continuous discharge and 5A pulse (2s on, 8s off). The Energizers have positive current limiting (PTC resistor) built into the battery for safety. Without it, the batteries could supply a lot more current but would get very hot. Perhaps this is what Canon were thinking of. I can imagine cheap Li AA cells from China with no (or unreliable) current limiting could certainly be a problem.</p>

<p>The built in current limiting is probably the main reason why flash recharge is slower than with NiCd or NiMH. I don't know how fast the new "ultimate" Energizer AA cells would recharge a flash, but it could be a considerably faster process than with the older "advanced" Li AA cells. Perhaps twice as fast since they can supply twice the current? Perhaps these newer Li AA cells are the reason for Canon's warning?</p>

<p>NiCd and NiMH batteries can deliver 5-10A (maybe even more) if not current limited, but I assume there's some sort of limiting built into speedlites or external power packs could blow them up!</p>

<p>The reason current limiting is needed in Li batteries is that they can go into thermal runaway (at least Li-ion batteries can, not sure about Li-FeS2). Above a certain temperature, a reaction can start inside the battery that creates more heat, so they get hotter and hotter until some final event stops it (like battery rupture).</p>

<p> </p>

<p>I just put a fresh set of four Energizer Ultimate Lithiums into my SB-910. Recycle time for M1/1 is still about 4.5 seconds. </p>

<p>Canon MIGHT be referring to using *rechargeable* Lions, and the very real dangers of multiple cells with different capacities. These types of incidents result in a cell being totally discharged, and having reverse current forced through it from the remaining cells in the pack.<br>

You can find out a lot more about this very real danger here:<br>

<a href="http://www.candlepowerforums.com/vb/forumdisplay.php?107-Smoke-and-Fire-Hot-Cells-and-Close-Calls-The-dangerous-side-of-batteries">http://www.candlepowerforums.com/vb/forumdisplay.php?107-Smoke-and-Fire-Hot-Cells-and-Close-Calls-The-dangerous-side-of-batteries</a></p>