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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:
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:
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.
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.
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