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post #68 of Old 04-14-2019
colemj
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Re: Realistic expectations for my house batteries

Gel cells are well-known for their lifespans. The downsides are very narrow charge voltage limitations (one modestly high voltage event can trash them), and they have relatively low charge acceptance rates, as well as relatively low discharge rates - so charging them fully takes longer than other types, and using them for high currents isn't ideal.

Two Group 27's is a small bank, and implies that your electric propulsion needs are modest. For a larger need, high charge acceptance rates becomes important because one needs to put a lot of current back into the batteries before next use. Or one needs longer times between usage to achieve full charge.

Lithium really shines in this application because it recharges as quickly as you can throw current at it, and it is happy to operate forever at partial states of charge if you can't throw enough current at it.

For a continually cruised, large boat, with modest off-grid charging capabilities, lithium becomes the only realistic way of achieving this goal. It is still a tough goal to reach, though. I'd really like electric propulsion to be more generally mainstream, but as it stands today, it is really only for smaller boats that are more lightly used (propulsion-wise).

Mark

Dolphin 460 Catamaran "Reach"

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