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Old 14-01-2019, 08:35   #1
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Lithium Starter Battery for 20HP Outboard

Can someone recommend a Lithium battery for our dinghy?

I am looking to buy a LiFe (Lithium Iron Phosphate) battery for an electric start/power trim 20HP outboard. Yes, LiFe are more expensive, but research tells me it is smaller, lighter, holds a charge longer, and is faster to charge.

My 20HP outboard requires 500 CCA according to the manufacturer. The battery sites don't even list outboard LiFe batteries under marine uses, and they all do searches based on motorcycle or ATV model info. I can't find one that is searchable by CCA.

Questions:

1. Will a standard Tohatsu 20HP charger be sufficient to keep the LiFe battery charged without overcharging?

2. Is there any reason to fear using this battery in a marine environment?

3. Can anyone help me locate the right battery for this application? Will this one work? https://www.batterystuff.com/batteri...tx20ch-fp.html It says it has 507CCA, but it's not clear how they rate their batteries.

Thanks,

Greg
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Old 14-01-2019, 10:40   #2
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Lithium Starter Battery for 20HP Outboard

There are any number of them that are meant to start Liter Superbikes and larger.
I had one on both of my bikes for years and they always worked, Id just buy one meant to start a 100+ HP motorcycle, cause Im sure it would handle a dinghy motor no problem, and they are way smaller and lighter than you likely imagine.

Yes that one will easily do the job, although it may be a bit of overkill and you may can get a better price elsewhere

Mine worked fine with the motorcycle charging system, which is nearly identical to a dinghy motor, just trickle chargers at best, not real alternators
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Old 14-01-2019, 12:25   #3
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Re: Lithium Starter Battery for 20HP Outboard

I have one on my mercury 9.9 with electric start. It overcharges the battery as it has no voltage regulation, only a rectifier. It will hit 17v unless you unplug it. Have tried a pwm solar regulator which helps but plays up when you pull current backwards through the reg to start the motor. I am looking for options. I think the 30hp and up motors have voltage regulators. I might try using some diodes on the regulator to stop the start current from going through it.
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Old 14-01-2019, 14:44   #4
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Re: Lithium Starter Battery for 20HP Outboard

I spoke with the dealer who assured me the rectifier will stop charging when the battery reaches 13V. He also said these are a very good option, but recommended using the watercraft/motorcycle version and not the lawn mower type.
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Old 14-01-2019, 16:11   #5
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Re: Lithium Starter Battery for 20HP Outboard

Search for "Lithium motorcycle battery". I would probably look for a Harley motorcycle battery. It is small enough and should be strong for your 20hp outboard.

Here is a website: Lithium Motorcycle Batteries

Here is a 625 CCA Harley Lithium battery: 625 CCA Harley Lithium Battery

Here is a 540 CCA Harley Lithium battery: 540 CCA Harley Lithium Battery

Here is a 500 CCA Harley Lithium battery: 500 CCA Harley Lithium battery
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