> Purpose of the reservoir cap is to hold charge and deliver it > with more of a force than a weak battery could. Olin would have fun with that line, even coming from Joe :-). Technically the statement is arguably correct as less voltage drop =3D more voltage available =3D more force. Voltage =3D EMF =3D electromotive force is about as close to force as we get in the analogy stakes. What was meant is understood, but eg "less of a resistance", "less impediment" [tm] or similar may be more useful. Or not. > A low ESR > (low internal resistance) type would be preferable, as noted. Yes, but probably not as vast a difference here as some places. The object is, of course, to not drop much voltage across the internal resistance so as to prevent droop of the voltage during the transmit pulse. > You'll see them specified in SMPS for example for that charge- > delivering reason Partially for that, Partially for noise. Partially for minimisation of internal heating. All relevant. > A low-leakage type could mean a power switch is not needed, > which is not just a design extravagance. It means that no need to > remember to turn it off because an insignificant amount of power > is used Yesish. Capacitor leakage of power supply decoupling caps is often not of vast importance when power is either available in bucketloads or not at all. Whereas here, as Joe notes - > I've several projects with nW PICs which simply sleep at less > than battery self-discharge. One here is 6 years old and the > capacity of the original 3 AA alkalines is still very good. The > terminal voltage has barely dropped 1 microamp is under 10 mAh/year. So at 3 years 1 uA at 30 mAh is well below the typical 2000+ mAh from an Alkaline AA. As Joe notes, shelf life determining self discharge is far greater. Even at 10 uA =3D 500 mAh in 5 years an AA Alkaline could be expected to have some useful life left. Modern Alkalines tend (from memory) to now be marked with 5 years + "best by" dates. That SHOULD mean they reatin a significant majority of their capacity after 5 years. Should. Russell --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .