On my old Oxygen rear hub I try to remember to turn the power down when going down steeper hills. I live at the top of a steep hill and have three main routes up it and choose the least steep so that my old rear hub motor is not labouring in bottom gear where hub motors tend to be least efficient.
With the e-bike motors I have driven, there are no gears, just the one fixed if you will!
I do not believe that most bike motors have gears. There may be one somewhere, probably exotic and expensive that does, but due to the way revs and torque are delivered by electric motors, the weight and cost of motor gears is simply not needed. It is a misunderstanding I have seen here before.
The only gears on most e-bikes are only there for the human to use. As its the human who labours in bottom gear, not the motor, it labours in the same gear!!
Maybe you are mixing up the two?
With regard to the hills, the only answer for you that I can think of is the second battery, and its not a cheap option as you say, but probably the best. I am a pensioner, so I know where you are coming from....
Or maybe you should walk up some hills to save power each day, give yourself more time....
For your next e-bike, I am told that some can now use the downhill stretches to recharge the battery while braking as well, as all electric cars do, that sounds pretty good.
Maybe someone here can recommend one of those...for the future of course....I myself have never even seen one.....!!
Regards
Andy
PS. On downhills, you do not need to turn the power down, just simply stop peddling, that way you will use less electricity than still peddling. The motor should actually use no power at all with the pedals "still"....