Not sure on the amp hour of the battery, ebike manufacturers tend to use watt hour. Makes comparisons easier as some systems run on different voltages.
Mine is a 625 which was the biggest Bosch did at the time but new version will be coming out with 700. Some of the Chinese kits are coming with 900. Bigger not always better though as the jump from 625 to 700 adds another kg of weight.
Tweedlove course was 20 miles and 3500ft climbing and I got back with 2 (of 5) bars left on battery, although I reckon it was close to dropping to 1. Estimated range was 6 miles. Course was pretty tough on battery and I used higher power modes than I might have normally because I was “racing”. My mate has a Shimano 630 battery and even though he was on the slightly easier shorter course, our batteries dropped at about the same rate, although interestingly, his estimated range was always way higher than mine. He also had 2 bars left but the computer reckoned he had 15 miles left.
Least it’s ever done was at Comrie on my own, where I did 20miles and 3000ft. Had one mile left when I reached car.
Only time I’ve ran out was at Glentress last year where I chanced my luck with an extra loop up to the mast (3 times total that day) and the battery died at the bottom of Zoom or Bust after 26 miles and over 4000ft. The mellow climb up the green, past the skills park is a different kettle of fish on a 25kg beast after a full days riding.
Less steep terrain is a lot less demanding on the battery though. Did 40 miles of Clubbytrails from the house with 3 bars left and 26 miles up round the Lochs at Dunkeld with the same left and that one was all off road. Less gradient meant I could keep it in Eco more.
I think one would be great for you Velo. You could get out without being worried about running out of energy or being knackered for days afterwards. Obviously cost is an issue, but for road and light trail use there are lots of add on kits available which can be adapted to existing frames.
The mate I mentioned earlier was a total skeptic until he tried one. His riding has really improved since he got one. Without being so tired he is enjoying the off road more and with getting longer rides in his skills are improving. They’re not for every ride but are great fun.