My disclaimers - normal rolling hills in suburban MD, heavier rider at 220. Carrying a second passenger frequently (high functioning autistic son - 125 and only going up as he finishes puberty) about 50% of the time about 2 miles there and 2 miles back for things. And other times - riding a bike to the store or farmer's market solo, but with cargo on the way back which is 6 miles there and 6 miles back.

The Pedego dealer I met with said the smaller battery should be fine for what I plan to use it for (on the test drive solo I used 1 pedal assist up moderate hills - with my son, I used 2-3 and throttle to start).

I cannot link yet, but you can google the Pedego Stretch if you're unfamiliar with it. And the battery choices are: 48V 13 AH and 48V 17AH

Any help would be useful. This is a huge purchase, but I think it would give me and my son more freedom and options for entertainment and fun.

Just replying to myself for more info - salesperson who works bike said smaller battery should be fine. Pedego said smaller works but always encourage to get the bigger one as it will last longer.

According to "theory", the bigger battery should provide a little better acceleration; that's what I recommend. I rode a "Stretch" for a few days and it handled my 180 pounds fine on rolling hills, but I hope you get a test ride with your son before you make a purchase and check the motor temperature at the top of a few hills. A core temperature of 180 -190 degrees max should be OK; my rule of "thumb" is to place my hand on the motor and if I can keep it there comfortably for 10 seconds, it's OK. A better system, of course, is a temperature gauge which you can fabricate. Maybe DW, C58 or Dilkes or someone has a better method.

I did ride it with him, but didn't think to check the motor temp. For that ride we used 1 assist for normal riding, 3-4 for going uphill. Most rides with him would be 2 miles to something - break, 2 miles back from something.

That shouldn't be a problem, and probably the smaller battery will be adequate.