Several new observations. Using an old 570, the battery cutoff is around 2.3 V (2 x 1.15) and much higher than on some of the newer Canon cameras. Interestingly when the current from the power supply is measured, charging the flash takes quite a bit of current. One other point, the contacts on the 570 must be made of some semiconductor material since the voltage drop from the battery compartment to the board is quite large.
On the battery side, someone suggested that the Kodak low internal discharge batteries were Eneloops, probably not since the Kodak ones are made in China. Data is being gathered but it takes two hours to test a single battery at 1A discharge so not as fast as I would like.
Bill
I realize this thread hasn't been touched in a while... but your findings make alot of sense.
1) If the Low Voltage Cutoff (Lvc) is 2.3 this means that the circuitry is probably designed with this as the minimum input voltage. Electronics typically run at 3v, 5v, and 9v and all circuits have input regulation to help protect from bad current sources. A good set of rechargeable batteries is going to start at 2.4v and if you hit it hard 5 or 6 times (flash) then pulling voltage down to 2.3v is very easy to see. The defining question would be to identify what the current consumption is for a flash charge cycle and then integrate that into testing. Most testing is done with constant discharge loads which is nice, but not realistic. Variable current demands are more the norm in most applications.
2) Alkaline and Lithium cells deliver a nominal 1.5v which means 3v and they drop off around 1.1v so setting your cutoff voltage for 1.15 per cell is a tad higher than the cutoff.
3) This helps to explain the move to Lion batteries which deliver extremely consistent voltage but can't be fully discharged. Lion also has a higher energy density yielding longer run times.
4) The slightly flatter voltage curve on the Eneloops would also explain why they are able to deliver a little more voltage and a little more current over a longer period. The lower internal resistance is as much as a factor of 10 from what I read. That would have a impact on the voltage being delivered. So while both cells can deliver power the voltage would drop.
5) Lastly, I suspect that as the batteries heat up the internal resistance changes. Again, to gather realistic data the batteries might need to be in a warm environment or be insulated and then hit several times. While it would bad for the case, it would be easy enough to run thin probe wires into a housing and fire the flash 5 or 6 times to observe what is going on with temperature profile, current demand, and voltage.
6) Strobes aren't as reliable as a comparison because it is essentially a capacitor charging system. Capacitors are much more tolerant of voltage differences and can easily work with 1v/cell. On the other hand, our cameras are actually embedded computers. As such they have logic circuits that depend on very precise voltages being present. Typically transistors work with either Negative, nothing, or Positive voltages and use 2 of the 3. Most computers work with -5 and +5 for their zero and 1 where as lower function computers use 0 and +5. the 3v ecology is very similiar. The core issue is that voltage fluctuations push the boundaries closer and can cause the electronics to make a mistake. So the demanding voltage requirements actually make a lot of sense.
7) I think this is one of those things where we sometimes just have to bite the bullet and pay a little more. When you look at all of the costs in going diving somewhere the batteries are really a minor cost. Diving is one of those hobbies like fishing where you can get some enjoyment out of it but the cost justification can be embarassing. The cost per pound of "free" fish makes a nice dinner at a restaurant look affordable. Likewise, the cost of the batteries is really incidental when compared to the cost of engaging in the supporting activity, diving. Furthermore, the end cost of getting it wrong is to experience battery failure during your dive which means you lose a dive and increase your "Dive Time Cost" or DTC.
DTC is this metric I came up with that basically boils down the cost of the equipment, training, and travel into a cost per hour (or minute) of actualy underwater time. DTC can be used to determine if a given piece of gear is a good purchase. Something that lowers your DTC is then justifyable. Fortunately I'm single and don't have to take that to the "honey-do" committee that meets at DWA (Dive Widow's Anonymous).
Nonetheless, I appreciate everyone's contributions to this. I was looking for confirmation that the Eneloops wasn't just marketing nonsense. In the process this thread answered a long running curiosity. I have a 2001 vintage Pentax Digital SLR that likes photo batteries and will run on AA alkaline or lithium but refuses to use NiMh batteries.
!! My point was simply that the small improvement that the low-discharge batteries offer shouldn't have been an (undisclosed) requirement for a few camera models here and there. That it has become so is seeming evidence of poor engineering, though I'm here to find out different if that's the case.
