To clarify, when discussing the low point 15% vs. 40%, what is meant is when the display reads zero, how much is actually left in the batteries. There is no way to measure that by observing the display.

I am not aware of NiMH's being harmed by going to zero however, the only reason I can think of are the voltage drop, and the cell variation, where some cells would be empty and other cells would force current through them, which is known to cause damage in NiMH's. So, to avoid those problems, the HCH leaves a reserve at the bottom.

Overcharging at the top is a definite NiMH killer, they cannot accept charge at high rates past about 80% full, so the HCH has a reserve at the top and will stop charging when the upper reserve is met. Again cell variation is a problem so the upper reserve point is likely to be lower than 80% when the meter shows a full battery.

So if your meter swings from full bars to zero bars, theoretically the battery only went from the upper reserve to the lower reserve point, figure less than half the rated capacity of the battery (6500mah on the HCH-I, don't know what it is on the HCH-II). So a 10% swing on the meter, is about a 5% swing in the actual battery capacity.

I recently discovered that the NiMH batteries that the HCH's use are rated for about 100k 5% swings, which compares very favorably with consumer NiMH batteries rated at 1000 full discharge cycles. Many small swings occur in normal driving. A naive calculation shows that 27 5% swings per day would yield 10 years of life. Accellerating gently from a stop to say 35 mph does not use 10% of my meter, although perhaps two of those would.

Course if I floor it and do a 0-65 leadfoot, I can use 30% of the meter in one go. :-)

I also used to have a problem with sustained hill climbing on my commute, if I camped in 5th gear, the display would drop to 4 bars every time before the charge cycle would start. My solution was simply to downshift. I don't think the CVT has this problem, although if you do have daily wild swings you could try 'S' (sport?) on hills to see if things improve.