How long will it go?

Run time is entirely dependent upon the current demand of the motor. At trolling speed the boat will run more than 50 hours. At water skiing speeds, we get an hour. The electrical system was specified to either run 25 miles at 8 mph or do a competition wherein a quarter-mile sprint at 26 mph was immediately followed by a five-mile race at 18-20 mph.

Below is a performance plot with two people aboard using the 11” propeller, which is great for towing and sharp maneuvers. This chart can be used to predict speeds and runtimes in semi-protected waters. Higher steady state speeds are attainable with the 13” pitch propeller and just one person aboard.

How long does it take to charge?

To meet the required performance, this boat has a 19kWh LiFePO4 battery. Expecting to use a 15A convenience outlet in the US (120VAC), an onboard charger was selected that yields 8.0 Amps. Therefore, if the battery is discharged to 50%, for example, it will require a 12-hour charge. This is adequate for our current needs (pun intended).

By allowing the use of a 20A outlet, the charge current can be halved to six hours. But, with each increase in charge current, more weight is added to carry the charging system; this is the limitation. Although the batteries can accept a maximum of 50 Amps charge current, the weight and complexity of that charging system would not be acceptable for our needs.

When people ask how long it takes to charge, I answer, “Every three weeks.” In practice, with frequent use, I charge the battery as described above every three weeks. Charging is as simple as plugging in and walking away. Unlike lead acid batteries, LiFePO4 batteries are just as happy sitting at half full.

Interestingly enough, more commonly used lead-acid batteries only allow a 50% discharge before causing issues (off-gassing of hydrogen and loss of capacity). LiFePO4 batteries may be depleted to 10% or less without damage or degradation. Furthermore, for winter storage, it’s desirable to leave LiFePO4 batteries at 50% without maintenance charging or removal to interior (warmer) storage.

Concerns about lithium-based battery life and lithium recycling

LiFePO4 batteries used in this retrofit promise 5,000 charging cycles. For a boat used seasonally (over seven months, for example) and charged once a week, that’s an expected battery lifespan of 166 years. Truly, the last thing we need to worry about at this juncture is lithium recycling. Even for EV autos, although the hype is about the negatives of lithium-based battery technologies and the cost of recycling is ubiquitous, I offer that an EV auto battery is expected to last 24-32 years, even with frequent charging.

What should be a much greater concern, and that which gets very little light, is the lead recycling of lead-acid batteries. There are at present only three lead recycling plants in the US. The one west of the Mississippi River is set to shut down, due to environmental concerns. Recycling lead-acid batteries is an actual issue, due to their comparatively short lifespan and toxicity.