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ely avatar image
ely asked

Lithium vs AGM

I plan to change my gel with lithium but I will leave the boat on the hard for 11 months per year for the next 5 years. After I will be on board 4 to 6 months a years. Has anyone any idea on what are the storage constraints for lithium and AGM knowing they will stay on board in countries there the boat will be at the time (. Mostly in the Mediterranean Sea). I will prefer lithium but it depends on how each system will behave for the 11 months. I have 400W of solar panels but I do not know if that will make a difference during these long periods. I will gladly hear any comment or advice. Thanks

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3 Answers
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machined answered ·

I'm no expert on batteries but I dont think the lithium will like being 100% charged for the 11 months you're gone. On the other hand, the AGM will love being 100% charged for the 11 months. The down side to AGM is that they will go bad fast if you take them below 50% but if you keep them above 80% then you get a lot of life out them. I would recommend 600ah of AGM. That gives you a 125ah of power before you go below 80%. That's plenty while you're there for 6 months and they'll love to be topped up while you're gone. Plus they're maintenance free.

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ely avatar image
ely answered ·

Thanks for your answer. What do you mean by maintenance free?

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seb71 avatar image seb71 commented ·

"Maintenance free" when talking about Valve Regulated Lead-Acid batteries (AGM or gel) means that you don't have to add distilled water (in comparison with Flooded Lead-Acid batteries/cells).

This can also be a downside if some Hydrogen does escape through the over-pressure valve (if charging the batteries with too high current), because you have no way to correct it (you can't add distilled water).

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Alistair Warburton avatar image
Alistair Warburton answered ·

Check out batteryuniversity.com for background... Every battery is a compromise, no matter how good.

Also any battery will have storage/maintennce requirements which if you dont adheer to will shorten its working life, considderably in some cases.

For example AGM are very susceptable to high voltage and high current, generally, basically if you get them too hot or let them gas you loose electrolite that cat be replaced. They also suphate, like all PB, if left partially charged for even modest amounts of time so maintenance charging with a carfully controlled voltage and schedule is critical. You may also find that cell ballance is an issue without regulay cycling as equilisation is tricky at best and all but imposssible without good temperature compensation.

Flooded cells need watering but then if you boil them a little, every now and then, they probably likely will not suffer.

And yes that is a HUGE generalisation... Check the specs of the speciffic batteries you are considdering. also check out other variants if you are considdering PB, lead carbomn for example.

If you have shore power when the boat is dry then a maintenance charge/ routine shouldnt be an issue but remember that all PB take at least 12Hrs to fully charge and if your solar only keeps up with self discharge every few weeks, in the winter, PB will suffer badly.

Hope that helps...

Al

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