Battery self discharge period?

C

chrisbitz

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Bromley, Kent - Sail in Medway
www.freyacat.co.uk
I've read about Battery self discharge here, 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?
 
3 months should be safe to use but it may be perceptibly down.
6 months won't do any harm but should be recharged before using.
Self discharge rate increases at higher temperatures, slows at lower.
 
Considered a solar panel?

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.
 
I find that my two Elecsol leisure batteries lose about 10-15% of their charge in the course of 3 Winter months. I give them a 24 h. charge in December and in April. They 've never left the boat in 7 years.
 
It varies.
It can be quite fast when batteries get old.
My motorbike battery won't start the bike if it's been left for a month, but is fine in every other respect. I charged it and did a capacity test and IIRC it was about 75% of new.
A trickle charge from a solar panel can help a lot. Even a small one.
 
VicS said:
Considered a solar panel?

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.
Click to expand...

Thanks for the suggestion - Although I'm a little concerned about the cost and additional wiring required - would a 5 or 10w solar panel still need the regulator and auto cutoff and all the gubbins, or is there something I can plug in as I leave, and then unplug when I arrive?
 
chrisbitz said:
Thanks for the suggestion - Although I'm a little concerned about the cost and additional wiring required - would a 5 or 10w solar panel still need the regulator and auto cutoff and all the gubbins, or is there something I can plug in as I leave, and then unplug when I arrive?
Click to expand...

A solar panel of that size does not need a regulator BUT make sure it has a diode to prevent discharge at night.
 
Chrissie said:
I have that one, its not waterproof, but it works well, cant leave it out because of the dew and the rain.
Click to expand...

One boat I sail on, we just have a south facing 5W panel inside a window.
It makes a difference for very little outlay.
Engine starts that bit easier in winter.
 
chrisbitz said:
thanks again for the brilliant advice!

http://www.maplin.co.uk/solar-powered-12v-12w-battery-charger-217850

I've found this one, it has a diode to prevent reverse charging, so this should be OK to leave plugged in to a 105ah 12v battery for a week or two?

I'm guessing that 12w counts as a trickle charge, and you can do that almost forever?
Click to expand...

Before you buy it, have a look at this one: http://www.sunstore.co.uk/12v-10w-Monocrystalline-Solar-Panel.html. Have a nose round their site. I reckon £50 or so should get you a 20w panel and a controller. That would do more than just top up your battery, it would go some way towards replenishing your usage day by day.

I have separate starter and domestics, so I fitted 2, 20w panels and a dual battery controller that sends 90% to the starter battery until burps then works on the domestic. Last week I came to the boat to find both batteries up above 13v inspite of a few VERY cold starts of a stubborn VP2003 and only very short runs in between the previous weekend.

I chose two 20s rather than 1 40 because the only place to put them is likely to be shaded by the boom quite often, and one shaded 20W and one in the sun will have a bigger output than one 40w part shaded.
 
Lonely Batteries

It'll be 11 months since last use,before I get back to the boat near Marseilles.Batteries were all new in late May 2012.Cruise finished July 2nd last year.Ill health of SWMBO since, but fixed up now.Everything disconnected at the battery poles.Hope to arrive 20th May next.
What are the chances of being able to spend the €360. on wine instead of replacing them all?I remember the boats charger is 16Amps Tecplus, three stage affair
I think the winter in Marseilles was not a repeat of the previous year, but there were a few nights of - 3C ish.
 
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chrisbitz said:
Thanks Steve, that's a really interesting site, I think I might go for a 30w kit for £69 - now I've got to figure out how to mount it and where - It might be best being removable when I'm on the boat, and just have it working when it's left for a week?
Click to expand...

A 30 watt panel is beginning to get fairy large physically and difficult to fit to a small or even not so small boat.

A common rule of thumb regarding the need for a controller is if there are 10Ah, or more, of battery capacity for every 1 watt of solar panel then a controller is not necessary except that a controller is usually recommended for panels over 10 watts anyway.

I have a 5 watt panel.. it was the largest I could fit permanently.... and a 60 Ah battery, They are fine and i have not had to take the battery home for charging since I fitted it. If I was going off for more than a weekend at a time I'd look for something larger to connect on a temporary basis.

I think I saw a 10 watt panel in Maplin that I could have fitted but I took one look at it and walked away!
 
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