Replacing AGM with Lithium on a single engine 22' Center Consul Boat

Q&A and troubleshooting
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Considering Switch from AGM to Lithium on Yamaha 250 SHO — Need Advice & Wiring Diagram

Hey everyone,

I currently run two 12-volt AGM batteries on my saltwater fishing boat. With electronics and a bait tank running all day, I’m finding that my AGMs are usually drained within 2 days. I’m thinking about switching to lithium for the longer run time, but I’m concerned about charging safely off my Yamaha 250 SHO and not damaging the alternator or the batteries.

I’ve seen marine lithium cranking batteries as well, but it’s hard to tell if they are truly safe/compatible for the SHO charging system.

Questions:

  1. Can I safely switch to lithium for my setup?

  2. Will the Yamaha 250 SHO alternator be at risk if I go lithium, and if so, what do I need to protect it?

  3. Is it better to keep an AGM as the starting battery and run lithium only for the house loads?

  4. Does anyone have a wiring diagram and parts list for doing this correctly (lithium house bank, AGM start battery, DC-DC charger, etc.)?

Looking for real-world advice from anyone who has done this on a Yamaha SHO or similar outboard. Thanks in advance!

2

Best Solution:

Retain a small AGM battery for cranking / Alternator Buffer.

Charge the lithium batteries from a dc/dc converter, or ACR if the voltage range is compatible.

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Lithium batteries disconnect IF the charge voltage or current get too high. You need to retain an AGM battery across the alternator in order to protect the alternator regulator. Most designs will burn the regulator if there is a sudden loss of battery at high speed..