I haven't owned my zero long enough to experiment with this but I read somewhere that the charge rate is not linear. So, if you were planning a trip that required charging, would it make sense to make your stop(s) when the battery will take a charge the fastest? I know it charges more slowly when nearly fully charged. Is the rate of charge effected when it is low?
When I ran my battery down to zero, it took a long time to recharge. It required 8 hours of continuous charging just to get the battery pack back up to 50%. My observation is that the pack charges faster when it is not so depleted and that is supported by the Kill-A-Watt meter, which shows a power consumption of about 1150 watts when charging an empty battery, which rises to 1350 watts as the pack nears being fully charged. So it would seem that you get more charge for your time if you don't wait too long to recharge during a ride.
Is it not a rising voltage system when charging the battery?
If Amperage stays the same and consistent throughout most of the charge, then for voltage to rise, wattage has to rise as well?
I don't think you're observing what you think you're observing.
Yes, that's correct. With a slow < 1C charge, a fixed-current charger will deliver more power into the battery as the SOC increases until it ends the bulk charge, which is typically above 90%. The bike has a slightly higher effective miles-per-hour charge rate at higher SOC, until it ends bulk charge. Probably not worth planning a trip around, but it should be slightly faster to charge 30 miles of riding if you start at 90% than if you start at 40%.
This changes when talking about a quick charge > 1C, where the charge rate is limited by battery temperature. Charging at low SOC will allow the battery to accept more current safely, and the effect is significantly more pronounced than the slow charging above.