Mixing AGM and Lithium batteries

[Rohan]

My boat has 4 x 12v AGM batteries total. All the batteries were stamped Sep 2007.

2 x AGM in bank 1
2 x AGM in bank 2

Bank 1 still has very robust voltage but bank 2 has failed and needs to be replaced. I think the previous owner used the boat very lightly and possibly was always switched on bank 2.

Some people would say "replace them all" but I'm not a millionaire and I don't want to replace things that are still working fine.

I am interested in switching to lithium batteries though, and am considering putting lithium in bank 2. Would that be any problem having mixed types this way? I can run the battery banks separately, or together.

[tkeithlu]

Can you charge them separately? They have different charging cycles.

Thirteen years? Consider some Durocell AGMs, available at a reasonable price from Sam's. That's a bunch cheaper than Li-ions.

[Adelie]

Never hook them together, they run at slightly different voltages. Combine them and one bank will drain to charge the other, even if that bank is already fully charged.

[SweareDeep]

These two sites have a good discussion of building lithium-lead hybrid battery systems:

https://www.zwerfcat.nl/en/lithium-hybrid.html
Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design

[Rohan]

Originally Posted by tkeithlu

Consider some Durocell AGMs, available at a reasonable price from Sam's. That's a bunch cheaper than Li-ions.

tkeithlu, you are awesome!!! Thanks for the tip! I ended up going to Sams.

I decided not to switch to lithium at this time. The only local places that had AGM batteries that were the right size for me were Marine supply stores and Sam's Club. The Sams version was so much cheaper it was well worth the price of membership even if I never shop there for anything else!! wow

If I wanted standard flooded batteries instead, both Costco and Autozone had incredible deals. But I wanted to keep them all AGM.

[Paradox111]

https://youtu.be/sqT27KbxRec
and
https://youtu.be/tAuPfgZgXec