Battery Self Discharge

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Hanalee

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China, Hongkong
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Electronic Engineer
Hi, folks
Recently, I've read about Battery Self Discharge Guide, and was wondering over what period of time it occurs?
I have a 12v 105 AH leisure battery on my boat with no charger, so I bring it home and charge it before every trip. If I left a fully charged battery on the boat, how long would it sit there, until it started self-discharging any significant amount?
Is it days, weeks or months? Anyone has ideas of it? Thank you in advance! :)
 
If you are using a lead-acid battery, you need to be aware that resting at even a low amount of discharge for an extended period (weeks to months) will lead to sulfation of the surface layers of the electrode which permanently decreases the capacity of the battery. In this reaction the spongy lead sulfate which can be easily converted back to lead during charging converts to a hard crystaline form which resists the charging reaction.
The rate of self discharge and the resulting vulnerabilty to sulfation depends strongly on the exact chemical formulation of the lead electrodes.
You might want to consider a small solar PV system to maintin the charge level of the unattended battery while it is on your boat.
 
On average almost regardless of chemistry secondary batteries lose about 1% a day. Primaries vary a lot. Mercury hearing aid style are very slow but the most extreme are carbon air batteries that have almost no self discharge rates.
 
paulengr said:
On average almost regardless of chemistry secondary batteries lose about 1% a day. Primaries vary a lot. Mercury hearing aid style are very slow but the most extreme are carbon air batteries that have almost no self discharge rates.
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Lithium-ion batteries discharge at a rate between 0.3 and 2.5% per month, depending on state of charge.
 
Thank you for you all the replies..
With only a meagre charging output from an outboard I used to have to bring the battery home periodically for charging. For my needs with a small Leisure battery a 5 watt panel has proved adequate to keep the battery topped up.
With a 100Ah battery or if the boat is used frequently or if the power drain is significant a 10watt panel would be needed probably.
 
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