DLuders, on 12 September 2012 - 10:16 PM, said:
As demonstrated by many AFOLs on this topic, the AA Rechargeable batteries' 7.2V is no match for new AA Alkaline batteries' 9V. That is what I was demonstrating in the video -- a 25% difference in voltage greatly affects ground speed. My AA rechargeable batteries were freshly-charged and new. The Lego Power Functions Rechargeable battery's 7.4V helps a tad because it is lighter than 6 ea. AA batteries.
Your video shows a clear difference. How long do the AA batteries deliver enough voltage to run faster than the rechargeable ones?
An alkaline battery starts out at about 1.6 volts (with no load) which drops to about 1.5 volt under a modest load.
Its voltage gradually drops from there to about 1.0 volt, at which point it is empty. So while a brandnew battery produces
more than 1.5 volt, the average voltage over its lifetime is well below 1.5 volt.
The rechargeable one drops from about 1.4 volt (fully charged) to 1.2 volt. On average, it produces 1.3 volt (which is more than
the nominal voltage) and it does not drop as much under a load.
In any case, the initial difference in voltage is less than 25%, and only decreases from there on (if both batteries are half-empty,
they'll produce roughly the same voltage, when both are almost empty, the rechargeable one produces more).
So the difference in speed is quite surprising, nevertheless, the video demonstrates it very clearly.
(PS. The 7.4 volt lego rechargeable battery, when fully charged its output is more than 8 volts).