I certainly found on Friday when a cold north wind was blowing over Edinburgh that my Lipo was not quite so "zippy" as usual, but I, and it, were still able to make a first attempt with 20" wheels and the Sram Sparc system on Dublin Street, all the way from the bottom up to St Andrews Square, with a rest both for me and the battery at the lights 100 metres from the summit. However, that same wind which was diminishing the battery was blowing on my back lending its own assistance. I tried a NiMh today (just to discharge it and keep it in good condition) but found that although the air temperature was higher, performance was sluggish even compared to the diminished frost-bitten performance of the LiPo the previous day.
As for range, I have given up trying to measure how far a battery will power the motor. With a pedelec-only system it is just impossible to keep the motor constantly on by pedalling at under 15mph for 10 to 20 miles or more, whereas with a throttle and no pedalling a more accurate measurement could be obtained. I doubt if the range on the Sram Sparc system is much affected by the rider's input at it appears to contribute no more or less than the rider himself contributes. Therefore in first gear going slowly up a hill the demand on the battery may be the same as it is on the flat pedalling and travelling faster. There are of course many other variables, and in a comparison between the NiMh and the Lipo the 10% over-voltage of the latter may give an impression of longer range simply because the better acceleration takes the road speed up to the motor cut-out point very much faster and then if speed can be kept at just 16mph, with the pedals in top gear for a while, no demand at all is made on the battery.
There are of course many other variables, and I now assume, as a simple rule of thumb, that a battery will do 15 miles, planning a trip on that basis, taking a spare if the range is likely to exceed that distance, or two spares, if likely to be over 30 miles.
Alex may not be too keen to switch to Lipo cells at present having just bought his bike but I can assure him that that 10% over-voltage and 1kg weight saving transforms the Sram Sparc system. He would no longer notice his bad back.