The longest I have done is 15 miles (out and return) with my 350 watt homebuilt with 24 volt 12 ah SLA. That was averaging about 11 mph with moderate pedalling. Some flat ground and some hills, a total of about 450 vertical feet between highest and lowest points. Some up and down hills in the middle that don't add into the total vertical, however. I didn't have my digital voltmeter at the time, but recharge took about 90-100 minutes at 5 amps, so I'm guessing it was about 8ah. A 10 ah lithium ion battery weighs less than a comparable sla, NiCd or NiMH, but that (relatively) small weight difference won't make up that kind of range difference. I agree with the others - flat ground, hard skinny tires and a lot of pedaling to go 40 miles on a 10 ah 24 volt battery - jd