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Old 05-22-2018, 03:25 PM   #8
DDW
Guru
 
City: San Francisco
Join Date: Apr 2018
Posts: 3,094
There are numerous vendors for lithium motorcycle start batteries, almost any of which would work on a small outboard. Everybody should please note that there are MANY different kinds of lithium batteries. The lithium polymer and lithium cobalt chemistries are the ones you read about in the newpaper as having started fires etc. The lithium chemistry used in motorcycle start batteries is lithium iron phosphate, LiFePo4 or LFP for short. This chemistry is far more resistant to thermal runaway which is the mechanism by which a Samsung cell phone catches fire. An LFP is a little heavier than the lithium polymer used in cell phones and RC planes, but far lighter than a lead acid.

A properly made LFP with built in battery management system is as safe or safer than a lead acid, while weighing 1/4 - 1/3 as much in an engine start application. Cost is 3x or so higher - but it will last perhaps 3 times as long too.
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