I would point out that my old canon A40 stated Lithium batteries should
not be used. They never said why and your guess is as good as mine.
I don't see a similar caution with my A95 and haven't looked at other
canon (or any one else's models.)
Dave Cohen

 Of course the voltage drop is a function of the current.  But I
wasn't discussing that.  The camera does not power off at a
particular current draw.  It powers off at its design voltage cutoff
point.  And yes, alkaline battery voltage drops considerably with
current because of its very high internal resistance.  Energizer has
it ranging from 150 to 300 milliohms for AA alkalines.  Assuming
fresh batteries delivering 1,000ma, the voltage drop would reduce
the approx. 1.5v to about 1.35v (voltage drop == I*R, or 1*0.15).
NiCd and NiMH batteries use *very* similar chemistry, and the
internal resistance is 35 to 45milliohms for NiCd AA cells and 30 to
40milliohms for NiMH AA cells.  With fully charged cells, the same
1,000ma load would drop the voltage by 0.035v (NiCD) and 0.03v
(NiMH), both far lower than the 0.15v drop of the alkaline cells.
The data sheets for these rechargeables show that they are for
650mAh NiCd AA cells and 2,500mAh NiMH AA cells.

 It should be noted that under high loads these rechargeables can
deliver voltages down to 0.9v and lower, even though when almost
100% depleted the open circuit voltage will be about 1.0v.  So for
fully charged NiCd or NiMH batteries, it appears possible for them
to be able to deliver very high currents, maybe 10 amps for 10 to 15
minutes for NiMH cells and a couple of minutes for NiCd cells.
Lithium cells on the other hand are current limited to only 2 amps
continuous current and 3 amps at a reduced 20% duty cycle (2 seconds
on, 8 seconds off).  Energizer doesn't give the internal resistance
for its L91 lithium AA cells, nor is the current limiting method
described,  but the internal resistance is certainly higher than
NiCD and NiMH batteries, given that Nikon's SB-800 has recycle times
of 7.5 seconds for lithium batteries whether 4 or 5 are used, and 4
second recycling times for NiCd and NiMH cells when 4 are used, and
when 5 are used, 3.5 seconds for NiCd and only 2.9 seconds for NiMH.

 I would have done that a year or two ago, but I've since found
that even when I shoot at a fairly high rate for several days
straight both my Fuji and Canon cameras won't need a battery change,
so I don't see a real need for standard 2,700mAh batteries because
the lower Eneloop/Hybrid capacities are still good for a couple of
days.  So now I keep standard batteries in one camera and Eneloops
in the other.  Eventually I'll use only Eneloops in both cameras.  I
always have lots of alkalines and a few lithiums on hand for
emergencies, even though I was never one of the Y2K fanatics.  :)

 Yep.  The voltage may be higher, but it's very unlikely that
lithium batteries have a lower internal resistance.  NiCd and NiMH
batteries have extremely low internal resistances.  Checking data
sheets, all battery types have their internal resistances stated
with a high and a low value, probably representing the resistances
of fresh/fully charged vs. the resistance when depleted.  The one
exception is lithium batteries, which don't include any internal
resistance values on the data sheets, but which give (for AA
batteries) a maximum sustained current of two amps and a maximum
intermittent current of three amps for a 20% duty cycle (two seconds
of current followed by 8 seconds of no current).  From the given
internal resistances, both NiCd and NiMH AA batteries should be able
to deliver close to 10 amps when fully charged.

 I've already posted what Nikon shows in its SB-800 manual for the
minimum recycle times of different battery types but here it is
again.  The SB-800 normally uses four AA batteries, but can hold a
fifth AA cell to potentially increase the number of flashes and to
reduce the recycle times.  For lithium batteries the recycle times
for 4 and 5 cells are the same, 7.5 seconds, probably due to the
lithium cell's current limit.  For 1,000mAh NiCd batteries and
2,000mAh NiMH batteries the minimum recycle times are 4.0 seconds
for both when four AA cells are used.  When five cells are used, the
NiCd recycle time drops to 3.5 seconds and the NiMH recycle time
drops to 2.9 seconds.

 

 Or put the batteries (lithiums?) in an emergency flashlight and
start using the Eneloops now.  In either case using the camera will
be free, but if you swap the batteries, in a few months the
flashlight's batteries will probably still be usable, increasing
your family's net worth by at least a few pennies.  :)