This is an interesting question since if the pulsed load hurts it would make sense to put a resistor in front of the load. This might make sense anyway since it would cause the system to restart if it gets stuck in receive etc instead of damaging the battery. I'm currently running a test to verify this.
Sorry for the late feedback...
As already stated, I use 2xAA batteries. I further need to reduce the power consumption due to a current module lifetime of only 3 month in ListenMode with a few infrared transmissions.
You are right that I do not need the cap for limiting the power surge/voltage drop like it is on a coin cell battery.
I am thinking about your cap solution with an additional series resistor to reduce the current peaks. I think current peaks(Listen 4µA -> RX 25mA) reduces the lifetime of a AA battery, doesn´t it?
The cited quote is actually joelucid's, not mine, but, in any case, AA can handle much larger current surges than 25mA (probably in the order of hundreds of mA) keeping in mind that they are probably not as 'elastic' as coin cells WRT to using mAH precisely because the chemistry is 'consumed' quickly due to the AA's low ESR. It also depends on whether you're using Lithium or Alkaline AAs.
Capacitors will help supply pulsed power, but, unless they are very large value caps, there is probably negligible effect on AA battery life (plus or minus) if caps in the order of 10-200uF are used in this application. The secret to this ultra-low-power listen mode implementation was Joe's realization that, in listen mode, he could set the duty cycle to an very low value using very high data rate (making the RX time very low, and the idle time
1000 10,000 times longer). That, and the fact, which I totally missed, that Idle Mode in the radio consumes 25% less power than Idle with WDT in the 328P.
You also won't need the power sequencing switches since the AAs can provide enough power at startup to get around the initial high current required by the uninitialized radio while the coin battery can't possibly supply this amount of short term power.
Tom
UPDATE: corrected duty cycle...