I had the same question initially. I believe it is 4-5 hours but you need to test it. The first time I didn't have a full charge and it didn't last long. After that I just used a 12V on the bike I had then. The RT doesn't have one so now I'm looking at hard wiring. Fact is, it may be possible to do many shorter day rides without a charger. Another consideration to try is carry a small power pack like some use for their phones when a wall charge is not available. In that case it might be possible to do long day rides and still have backup power. Anker products and others have newly advanced small power packs for phones and laptops that fit in a pocket, or maybe along your handlebar.