More 600EX-RT/Battery questions...fun!

Question

Greetings all!
I've seen several discussions about batteries and the flash, but I'm just trying to get the "definitive" answer
I've got two 600EX-RT's. The first one died on me at Christmas last year. While shooting, I discovered that the batteries became hot...really hot. The next time I tried to turn on the flash...nothing. Brand new batteries did nothing.
I had some extra money at the time and my flash was almost 2 years old so I bought a new 600 in January. While shooting with it about a month ago, the same thing happened. The batteries got so hot that, after I took them out and put them into my pants pocket I had to take them out because they were burning my leg!
That flash was still under warranty, so I sent it in and it's fixed now.
I have always used non-rechargable batteries...and I've used the Duracel Ultimate, for the most part...or the Eveready version. Don't remember the name, but I've always bought the "strongest, longest-lasting" type of whichever brand, on the theory that "The stronger the bettery, the longer it'll last".
Are rechargeable batteries better for the 600EX-RT? Are they worse? What's the Straight Dope?

Answer 1

TCampbell wrote:
I use rechargeable Eneloop batteries.
Eneloops are low-self-discharge.  A regularly rechargeable battery will drain merely sitting unused at a fairly quick rate... quickly enough that a few weeks after charging it will have lost quite a bit of power.  A low-self-discharge battery has a shelf like almost like a non-reusable battery... a year after charging they still have about 90% of their charge.
That means if you charge up some batteries to be prepared for the next time you need them...  you don't have to worry that they'll be very low or drained the next time you need them.
I too use Eneloops - the black professional series. My experience so far suggests that their low-self-discharge characteristics are somewhat exaggerated: they appear to lose power on the shelf at about the same rate as the "Enercells" sold by Radio Shack. But the Eneloops have been very reliable.
But I am a bit worried about these batteries becoming "hot".   When batteries are either charging or draining, they'll get a little "warm" but generally not "hot".  Usually "hot" means you're draining the batteries very quickly.  Were you running the flash hard?   If you _do_ need to run the lights hard (rapid fire and high power levels) you can split the load across multple flashes (there are mounts that will let you cluster 3 or even 6 flashes on one stand.)
All modern Canon speedlites are supposed to automatically shut down for a few minutes if the flashtube starts to overheat. (I've had it happen to me.)
But batteries overheating are a different matter. A battery overheats when the current flowing through it is too high. What may be happening is that as the batteries deplete, they may be unable to maintain their rated voltage (usually 1.5 volts each for non-rechargeables). The light, which expects to consume a given amount of power (watts) to recharge itself, may be forcing the batteries to deliver that power by increasing their current flow. (Remember that watts = volts x amps.) The batteries should be able to resist that demand, forcing the light to recharge more slowly (or not at all). But if they can't, they will overheat.
Fill disclosure: I'm not an electrical engineer. So the first person who identifies himself as one should probably be listened to instead of me.
Bob
Boston, Massachusetts USA