tpatana wrote in post #15429692
True, but for using them the voltage level 1.5V vs. 1.2V is the only one that really matters. And it's really rare to find a device that doesn't accept rechargeables instead of standard batteries. I never owned one, and I'd be curious to test device which is claimed to fail with rechargeables.
The simple fact that an item "accepts" rechargeables does not in any way imply that they are ideal. In a two cell arrangement, such as is under discussion here, circuitry is very often designed to cutout completely when voltage drops below a certain level. Where there is no cut-out circuit, units can become unreliable performers - often the case with radio triggers.
When prime condition rechargeable AA cells come off the charger, assuming an 'intelligent' Minus Δ V (-δv)* charger rather than a less reliable thermal cut-out type, they have a voltage of 1.4 to 1.58v. As the cell cools to ambient temperature, the voltage drops to the notional** 1.2v marked. Within a relatively short period of time (hours rather than days or weeks) the actual voltage declines slightly to somewhere in the region of 1.1 to 1.15v. Place two cells in a chain and the starting voltage of your unit is likely to be in the 2.2 to 2.3v range.
*While usually sold as 'intelligent' chargers, these are not without their failings for NiMH cells as the voltage change at 'full' is notoriously difficult to detect; variable as a function of charge rate and internal temperature.
**Notional in the sense that this is the intended average voltage among a selection of these cells but it is not an absolute value. Variations can and do occur.
If the 'low voltage' detection of the circuit is designed to function at (eg) 2.0v then you have very little overhead. If, as frequently happens, one of the two cells in your chain is a little under par, you can quite easily find that you have put freshly charged cells into the unit and yet performance is compromised. With some circuits, the item will fail to switch on or will only function momentarily (my wife has an Olympus P & S which does exactly this). In other cases, as with radio flash triggers, while the unit may appear to be fully funcional; in fact the performance is compromised and they become unreliable. This despite the fact that "freshly charged" rechargeable cells have been used.
On the other hand, alkalines start off at a notional 1.5v so a 2 cell chain has a notional 3v as a starting point. This gives you much greater overhead and far more scope for voltage drop before any irregularities in use become apparent. Many of us have proved for ourselves that YN-622C, Pixel King and (as mentioned in David Ward's post, above) Pocket Wizard ControlTL FlexTT5s are sensitive to voltage in terms of reliability. And that is what we seek, reliability. If this means using single-use alkalines rather than rechargeables then that is a price I for one am more than happy to pay. A pair of alkalines in these triggers is likely to last months under even the heaviest of use, hardly expensive! This is the only place where I don't use high quality rechargeable cells - simply because they are neither as good nor as reliable.
tpatana wrote in post #15429692Also for flash use, the rechargeables give plenty more current, so they recharge flash much faster. So for flash use, they are preferred instead of normal batteries.
I wouldn't argue with the intent of your assertions here, but feel that in the context of flash triggers (the topic of this thread, after all) introducing this matter is likely to lead to confusion. Flash triggers do not require "plenty of current".
