In a nutshell Alex;
Neither Kalkhoff or any of the other mainstream suppliers are behaving in a grossly misleading way. They are merely quoting the cell maker's stated capacity. In practice due to the Peukert effect this is only applicable in the ideal conditions at lowest power usage, for example a light rider in Eco mode in still air and on flat territory. This is, as I've already said, no different from car mpg figures and e-bike range figures, both often given as optimums. That is a suppliers right, since they do not and cannot determine the usage conditions they can state the best one, even though very few can ever achieve that in practice.
As you rightly observed the crank units like the Impulse etc are less greedy than hub motors in general so wouldn't suffer as big a loss as that 30% on the test hub motor I quoted, but I'd expect on a derestricted bike like yours when used to the full that the capacity loss would still be in the region of 20% due to the Peukert effect. What I think you may not be appreciating though is the corresponding gain. That is if you use your system to the maximum for greater speed, although the consumption rate will reduce the measured wattage issued from the cell maker's specified figure, the speed you gain in the reduced time taken for that consumption will increase the distance travelled in that time. Therefore there is a self-cancelling effect, less time at higher speed can produce the same distance so range is not a reliable indicator of what total wattage a battery issues. You need something like a Cycle Analyst to accurately measure that.
Now the battery size issue. There have long been some e-bike options on the market with much bigger batteries, so it's not true that customers have never had the option. Several companies have offered 16 to 20 Ah as options and the odd one or two as standard. The fact is that it hasn't been a popular option and that is why most e-bike companies don't bother. Most customers don't need very long ranges so don't want to pay for very large and heavier batteries. Just look at how very many makers offer 8Ah options, including Kalkhoff on the Impulse and other systems. They do that because the demand for less exists, so they satisfy it.
In fact smaller is better for many numbers of users for more then one reason than initial cost. Take your Impulse system for example, the two main batteries offered being 11Ah and 15Ah.
Kalkhoff-BMZ state the achievable lifetime capacity of the two are as follows:
11Ah = 348,000 Wh
15Ah = 259,000 Wh
Which they calculate into these achievable lifetime total distances:
11Ah = 77,000 km
15Ah = 58,000 km
That means 33% longer life from the smaller battery. So the buyer of the smaller one if that is all they need pays £100 less in the first instance, and if a 15Ah would have been at end of life at 3 years, the 11Ah would still have another year left in it at the same usage rate. Gain, the £100 plus a third of the 15Ah cost of almost £600 currently, total £300, very worthwhile.
Why the longer life of the smaller one? It uses exactly the same physically sized 18650 cells but 2.25Ah instead of 3Ah, so each with 25% less content density. That means reduces operating temperatures under load and during charging due to lower cell internal resistance, and it's higher temperatures that chemically age the cell content. As a bonus the smaller content cells have 40% less capacity loss annually than the larger content ones when in storage.
So for the many users who only need what the standard Impulse system delivers with the 11Ah battery, it's win-win all the way.
Alex, on the 1, 2 and 3 points I've been more than fair in fully answering each time, but I don't wish to carry on having to constantly repeat the same facts time and time again, so I hope you will understand when I say this post has contained my final words on those.
If you wish to discuss the size and life issue that I've just raised in the latter half of this post I'm happy for that discussion to continue.
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