First question. Can any of you provide a good Ebike 101 type link? I have read here and there, but still find myself with more questions than answers. When I think I have answers, I look at a specific bike and am not sure the answers apply to the specific systems on the bike in question.
Poke around here:
https://www.electricbike.com/
https://electricbikereview.com/
Questions now:
1. Are Specialized (and other manufacturers private label) motors and batteries rebadged?
Spec tends to make their own inhouse stuff, but yes, most of them are Bosch, Yamaha, etc...
2. Assuming a 250 watt motor and maximum pedal assist setting, would a 3 mile average 4% grade be doable for a casual cyclist?
Really, a 36v motor is 350+ watts, and a 48v motor is 500++ watts, all depending on current.
A strong cyclist can pretty much equal the power output of a basic 36v system. Most 48v systems are going to be much stronger than any non professional cyclist.
3. I see max speed listed as 20 MPH on the bikes I am most interested in. Will they go faster on long downhills?
Good question. That is the power the motor assist cuts off at. Yes, it will go as fast as you can get it to go with the motor turned off, its just not going to give you any boost over 20mph.
4. It looks like some battery packs are very unique in size and shape. That gives me concerns about replacement availability in the future. Is that a valid concern?
Uh, yeah. I would be concerned. Ask about the cost of replacement batteries. Mine tend to last 3 years even if I don't use them much (they would probably last longer if I used them or charged them more often).
5. I am sure I want to do a mid mount. Does the battery location (down tube or rear rack) location make any practical difference given the stated use?
Good question. Down tube gives great weight balance. Putting a battery on the rear rack makes it very top heavy, rear biased and awkward. It sucked (IMHO). I did that once, but hated it, so I moved the batter to inside the frame triangle.
6. I guess the major systems have been out long enough to give us a glimpse into their reliability. It seems like reliability is good. Are there any common trouble spots with batteries, motors or computers?
Sooner or later you will probably have to replace the battery, so keep that in mind. They can last a long time if properly maintained.