I just had a long talk with the designer of the NiteRider Xcel Pro system about the matters that we've been discussing in this current thread. Here's what he told me:
Fuel Gauge operation:
When a new battery is connected to the fuel gauge, at quick test is performed by putting the battery under a load and measuring the voltage. The results of this test allow the the computer to decide if the 2.8 AH battery is in one of the following three states:
Fully Charged (this is determed if the battery is between 50% and 100% of capacity)
TOO LOW TO USE
If when the 2.8 amp hour battery is connected it is between 50 and 100% full, it will be judged to be "full", and the fuel gauge then measures how many amp hours the battery puts out. When it detects that 2.8 amp hours have been used up, it says the battery is empty.
Thus, if you hook up a fresh 5 amp hour 13.2 volt battery, the fuel gauge will read "empty" when the battery is only half discharged.
Emergency Power Mode
The Fuel Gauge is NOT used to put the Xcel Pro into Emergency Power mode. Thus, even tho the fuel gauge is reading empty, the Xcel Pro will continue to happily work with a 5.0 amp hour battery and will NOT go into emergency mode. For emergency mode to be activated, the thing senses the battery VOLTAGE.
The smart charger of the Xcel Pro checks to see if the battery is empty. If so, it charges it at a rage of C/10 (with respect to a 2.8 amp hour battery!!!) for enough time to fully charge the battery, then drops back to a C/30 rate (with respect to a 2.8 amp hour battery!!!) to maintain it. That's 280 ma "fast charge" rate, and about 93 ma for maintanance rate. If you hook a 5 amp hour battery to the thing, it will be charged at what, for it, will be more like a C/20 rate until it's been filled up with 2.8 amp hours worth of power, and at that point, even tho it still needs another 2.2 amp hours, the Xcel Pro charger will drop back to 90 milliamps, which is close to a C/50 rate. Thus, the thing will be charged to half C over a period of about 20 hours, then to fully C over the next 25 hours, making time to fully charge a 5 amp hour battery with the Xcel Pro charger something between 40 and 45 hours! The fellow who designed the Xcel Pro recommends that IF you insist on using a battery with bigger capacity than 2.8 amp hours with the Xcel pro, USE A SEPARATE (preferably SMART) charger for it.
The fellow who designed the Xcel Pro recommends one uses as a spare a 2.8 amp hour 11 cell (13.2 volt) battery packs. This because then both the fuel gauge and the "smart" charger will work properly with both battery packs. But as noted above, if you choose to use a larger capacity (amp hour) pack as your secondary pack, the system will work, but your fuel gauge will prematurely call your battery "empty" and your built in Xcel Pro "smart charger" will be VERY slow to charge your battery, taking over 40 hours to charge 5 amp hour battery.
The designer also notes that the battery pack supplied by NiteRider with the Xcel Pro is made with the highest quality Sanyo batteries they could find. It is made with better batteries than those used in the NiteRider Classic and Commuter. He regretted that NiteRider's advertising / marketing campaign did not emphasize this.
Other NiteRider news:
The LEDs used in the 19 LED taillight that goes with the Xcel Pro system are 12 degree angle, 4000 mcd rated LEDs. They are run rather "hard", in that because they are pulsed, maximal current (and then some) can be pushed into them, increasing brightness and efficiency further.
NiteRider is experimenting with... indeed has working prototypes of, I'm told... a novel arc lamp bicycle lighting system. This system, it is rumored, uses a pulsed Xenon strobe. I'm told that intensity on this can be varied from 0 to 100 per cent with little lose in efficiency at any percentage of full power. Unfortunately, this system would be very expensive to retail, and NiteRider does not yet know whether it would be profitable to actually produce it as a mass market product.
NiteRider discontinued carring the Black and Decker power supply charger because, in part, they ran into "reliablity problems" with it. They were buying Black and Decker chargers, I'm told, in quantity 100. I'm still rather suprised at the high dealer and retail prices they were charging for the modified charger, tho.
NiteRider is considering supplying a "semi-smart" charger with all their lighting systems. This would basically be a simple timer system, that would charge the battery at C/10 for 14 hours, then at C/30 after that. It would include an indicator light for on / fast charging / trickle charging. I'm told it would add $10 to the cost of their products that currently offer a totally dumb charger. I strongly urged them to go ahead and do this!!!
P.S. The fellow at NiteRider wanted me to remind ALL that the Xcel Pro is designed around a 13.2 volt battery, and WILL NOT WORK WELL with a 12 volt either lead acid or NiCd battery!!!