A 709WH battery would likely be a 48V15AH pack, Batteries shut off at 40V, so you have 10-15% of capacity left. So I would estinmate there's 600WH useable here, How far can you go on 600WH? On pavement with smooth tires, 50 miles is easy at 12 mph, With a mountain bike on knobbies, carrying camoing gear and also going 10-12 mph, I would guess about 30 miles.

Taking Atlas' post, it would be fair to say a 200W panel should deliver 150W to a battery in good sun, if it has an efficient charger connected up. Figure at least 4 hours to recharge 600WH,
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You might have to rethink the riding for 2-3 days. It's more like one day of riding and you have to break camp at dawn to catch the good light for recharging, Might have to carry a second battery, Anyway, this sounds like fun. If you do it, a report would be appreciated.





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