Charging Lithium Iron Phosphate Batteries


We are going to start cruising on our sailboat soon and I am looking for some help with our battery situation.  Currently we are using 4 interstate 6V lead acid batteries in two separate banks.  Our daily usage is about 100 to 125AH and I will also be adding to our solar for a total of 300 watts.  My question is more specifically about our alternator charging.  We have a 30hp yanmar with a 35amp alternator that puts out 13.6 volts.  If we go with lithium batteries I am assuming this alternator won’t work as it needs to put out 14.4 volts or would we be better off going with firefly batteries?.  Will a DC to DC charger somehow compensate for this loss output of my current alternator?  My other concern is burning out my alternator.   Any advice would be greatly appreciated.   - Dave


Hi Dave, your hunch is correct. Switching to Lithium is a not a  drop-in replacement and the alternator ability to charge your Lithium without burning out and also not overcharging your batteries is a very legitimate concern. If you are going with Lithium batteries, you’ll need a alternator that can handle full output to recharge your lithium batteries. A stock alternator cannot handle this. Also you’ll need to get a external regulator connected to your new alternator to charge a lithium at the correct charge curve.  - Jeff

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