I been wanting to try this for a while... running my propulsion system off one of my ebike batteries. They are 48v, same as my boat voltage. 20ah, lithium. In the first pic, the ebike battery is sitting on the uncovered FLA bank and actually turning the prop over. Connection is just small jumper cable clamps. In the foreground is my new not yet mounted instrument panel. Old (red) tach, and new (blue) volt/amp/power and power used all-in-one meter.
Second pic is screenshot from OpenCPN on my Note 3. I didn't think to start OpenCPN up until I was well out of the harbor. My track is the purple line. There is a break in the track from me fumbling the phone and killing the app. I ran on the ebike battery from my slip, out to the old Pontchartrain Park site, victory lapped around a piling and came back. The battery died a few hundred yards from the harbor entrance. Total run time at 250w was about 3:20, speed about 1.7kt. I might have made it all the way back in, but I had depleted the battery slightly while still at the dock. At over 10a discharge, the battery cuts off. There is a breaker or maybe a solid state circuit inside the pack. So I decided to do a run at 5a or thereabouts, or 250w since I have a watt meter now. This is all measured between battery and controller, btw.
I didn't want to take a chance on the battery going flat while maneuvering in the harbor, so I had another ebike battery standing by, and switching was a simple matter of unplugging and plugging a household/computer appliance cord connector. I was going to change batteries anyway, right at the entrance, just in case.
Total distance ran was about 7 miles, I guess. and about 6.5mi on the first battery, after some considerable drainage at the dock before leaving on this little jaunt.
No I am not advocating running your full size boat on a 20ah ebike battery. The Redneck in me is always looking for stunts like this to do, is all. But for someone who only needs electric propulsion for docking, especially on a racing sailboat where weight could be an issue, it might make sense to use one or two. Stow anywhere, use upside up, upside down, sideways, diagonal, whatever. But the best application might be for "microboats", such as canoes, kayaks, small dinghys, homebuilt small pontoon boats or catamarans, etc. This would be a good way to repurpose a battery from an ebike that no longer gets used or has a fried controller or something.
These things have their own self contained BMS, and generally ship with a charger. The 20ah 48v size is easily carried in hand or backpack. Typical weight is around 20lbs, and prices for this size start at around $450 on Fleabay. A little pricey, but remember it has a BMS and charger so that takes the sting out, a little.
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