Battery Buffs - answers please!

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viva

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I have a starter and domestic battery and a mains charger. My marina does not allow boats to be connected to the mains while the owner is absent. Obviously I charge the batteries when I arrive. If I leave the boat with the batteries fully charged and then leave them off charge for say 2 or 3 weeks, will the batteries retain their charge and is this regime detrimental to battery health vs leaving them permanently on mains charging? Thanks for your responses
 
If your batteries are in good condition they will be fine left for three weeks. It would be nicer to keep them on charge but if the marina doesnt allow it you have little choice other than to install a solar panel or wind turbine.
A 20w panel off Ebay for £30 and a regulator would solve the problem. I am in the same situation with my marina. my batteries are always fully charged when i plug in on arrival on a friday evening
 
Sorry, I'm not battery buff (is anyone that sad?), but leaving them for two or three weeks will do no harm providing they're fully charged when you leave the boat. All batteries self-discharge. It depends on the precise type of lead-acid you have, but something around 5% per month would be typical, although it can be higher.

Personally, I think the marina has a point: leaving mains chargers plugged in but unattended 24/7 carries some risk.
 
viva said:
I have a starter and domestic battery and a mains charger. My marina does not allow boats to be connected to the mains while the owner is absent. Obviously I charge the batteries when I arrive. If I leave the boat with the batteries fully charged and then leave them off charge for say 2 or 3 weeks, will the batteries retain their charge and is this regime detrimental to battery health vs leaving them permanently on mains charging? Thanks for your responses
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Provided there is no drain on the batteries and they are in good condition there will, as geem says, be no problem over 2 or 3weeks. Even 2 or 3 months should be no problem.

How do you think people on moorings, where there is no access to shorepower, manage?

A small solar panel will keep your batteries fully topped up if necessary, but you will need either two panels, one for each battery bank, or a dual output controller if you are to avoid leaving the batteries connected to each other in order to use a single panel unless you can utilise an existing split charging system.

FWIW I find that a 5 watt panel is more than adequate to keep a 60aH leisure battery fully charged.
 
VicS said:
How do you think people on moorings, where there is no access to shorepower, manage?
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And what about all those batteries that sit for months on shelves in Halfords and in warehouses? They always seem to work and won't have seen a charger since they left the factory.
 
I'd have thought that as long as you plug in for maybe 15-30 minutes each time after returning to your berth to make sure they are fully topped up before departing they would be fine - as you probably motored back in to the marina they'll already have had some charging from the alternator.

In winter I put a charger on for a few hours every month.....
 
Fully charged batteries are OK for several weeks before you notice a loss of charge and several months before damage is a real risk.

The big question here is how do you make sure they are fully charged when you leave them? 15-30 minutes or a bit of motoring back to the marina will NOT ensure that.

If you have a smart charger/smart alternator regulator you can get up to 80-90% capacity in a few hours depending on what level of charge you started from. That is not fully charged. Getting from there to full charge takes a good few hours more.

After a trip I like to leave mine on charge for at least 24 hours. I do disconnect then, leaving them on permanent float has no benefit if they are totally isolated.
 
A few weeks not on charge is not going to kill the batteries provided they are not draining significantly either, but most experts seem to agree that a constant trickle charge will extend the life expectancy of the battery - which has to be a good thing given the price of a decent one.

When we were in your position, we bought a cheap solar panel from Maplins - about 15w, I seem to remember and it cost around £40 in their sale. I added a cheap Maplins charge regulator - another tenner - and the result kept our engine and domestic batteries topped up all the time.

Don't go for a wind generator - very expensive for very little output - solar panels are a far more efficient way of generating some power. I didn't want to go fitting one permanently to the hull - looks ugly and gets in the way. I fitted a simple socket in the cockpit locker and just stood the panel on the cockpit floor while we were away - I'm sure that it wasn't operating at peak efficiency, but it was good enough to keep our batteries healthy.
 
I've known batteries to hold charge for years but it does depend on the battery technology and condition. A month? don't bother thinking about it.
 
maby said:
most experts seem to agree that a constant trickle charge will extend the life expectancy of the battery
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I honestly believe that is out of date advice.
It was certainly true in the days when self discharge was a real problem due to high antimony content and impure materials.
A modern lead-calcium or lead-low antimony battery has such low self discharge that if there is no load on it whatsoever, permanent float gives no advantage.
Being pedantic, the last thing you want is a "trickle" charge in its generally accepted meaning (in the industry) of a small constant current. That is potentially a recipe for water loss as the voltage climbs to maintain the current. If anything, you want a constant voltage float charge.
 
Troubadour said:
I honestly believe that is out of date advice.
It was certainly true in the days when self discharge was a real problem due to high antimony content and impure materials.
A modern lead-calcium or lead-low antimony battery has such low self discharge that if there is no load on it whatsoever, permanent float gives no advantage.
Being pedantic, the last thing you want is a "trickle" charge in its generally accepted meaning (in the industry) of a small constant current. That is potentially a recipe for water loss as the voltage climbs to maintain the current. If anything, you want a constant voltage float charge.
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I agree with this
 
Interesting replies!

I am NOT an expert on batteries or electrics, so when I recently wanted to buy a Ctek MXS 5 charger to charge my 110amp starter battery I phoned them and asked pacifilcally are they ok to be left 'on' while away from the boat which they confirmed was perfectly ok.

I know of at least 5 other boats in our marina with Ctek battery chargers left 'on' while their owners are away.

So now I am really confused!!

Mike
 
As Troubador says, if you can't charge them in your absence, the problem is to be sure your batteries are fully charged when you leave them. The solar panel + dual controller system solves that problem provided you get enough capacity. Mine's set up to send 90% to the starter battery until it's full then turn it's attention to the domestic one.

Even in the grotty "spring" we had, my batteries are always fully charged when I arrived at the boat the week after being on board for a few days with no other charge and, provided I don't ovedo it with the cold box, my 40w of panels keep up with use at anchor in the summer.

Using rigid panels, a 40w set-up needn't cost much more than a marine smart charger and means you're largely independent of external power supplies (until you want to run a fidge)
 
Caer Urfa said:
Interesting replies!

I am NOT an expert on batteries or electrics, so when I recently wanted to buy a Ctek MXS 5 charger to charge my 110amp starter battery I phoned them and asked pacifilcally are they ok to be left 'on' while away from the boat which they confirmed was perfectly ok.

I know of at least 5 other boats in our marina with Ctek battery chargers left 'on' while their owners are away.

So now I am really confused!!

Mike
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It's not a good idea at all if you have a charger that goes onto timed boost every time it is switched on (e.g. many Sterlings and Cristecs). If the marina supply gets outages or other boaters unplug you then plug in again, your battery may suffer from over boosting.

If you have a charger that detects a fully charged battery and switches off the boost quickly - and I think at least some of the Cteks are like this, then it's OK but still unnecessary, no advantage, particularly for a starter battery.

Only exception is that there are a few specialist genuine deep cycle batteries around - I'm not talking about leisure ones, I mean real heavyweight industrials, for fork lifts, floor sweepers etc that are discharged daily - that still use high (ca 8%) antimony content to help achieve good cycle life at the expense of higher self discharge and shorter float life. These will benefit from being left on low voltage float. Trojan T105s - not the lighter weight Trojans - just about fall into this category, they are borderline.

Edit - Having looked it up, I see you are only looking at a 5A charger for a 110Ah battery so damage potential is limited anyway.
I assumed the OP is talking about domestic batteries where you would normally be recommended to have 15-20% charge current capability.
 
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Will a suitably sized solar panel bring a battery up to full charge over time? I read a rather confusing and technical post on a motorhome forum which suggested that, without 16 hours of mains charging, batteries would never be fully charged. Any truth in this?
 
Some dear friends, who are now in Fiji with their boat, have asked us to look after their caravan at their olive grove whilst they are away. They have a single deep cycle battery in the van, topped up by a solar panel (they also have a genny when they're here). The battery was fully charged and then disconnected, it's been retaining it's charge extremely well over the last 6 months, I've had the solar panel connected (for a few days each time) only three times this year. I wouldn't worry.

I think the marina is right too. We have a yacht that's been on the hard here since last October, no power was connected whilst the owners were away. They came back, connected the power, and a few days later, fortunately whilst they were aboard, they smelt smoke. Investigation revealed a fire just starting behind a seat-back cushion caused by water seeping in over the winter and soaking a poor electrical connection. No damage was done but this could have been catastrophic had they not been aboard. In the winter boats are packed in here as close as possible, had she caught fire then it could have been a disaster. The good news is that one of the yachties here is a qualified sparky, so he had them sorted and elctrically safe pretty quickly.
 
HiAndDri said:
Will a suitably sized solar panel bring a battery up to full charge over time? I read a rather confusing and technical post on a motorhome forum which suggested that, without 16 hours of mains charging, batteries would never be fully charged. Any truth in this?
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I can't see why it wouldn't. Over several weekends fettling the boat on my mooring during the spring, with no other charging, my solar panels seemed to keep the voltage up where I'd expect it to be if the batteries were fully charged.

I suspect that the discussion referred to those daft little plug-in-the-fag-lighter things with a 5w (at best) output. If so, they'd be right. If you're lucky, they'll keep up with the self-discharge and the memory for the radio, but electrons is electrons, and, as long as there are enough of them flowing in the right direction, the batteries aren't fussed where they come from.
 
I don't know why this thread continues. It's not a problem, start the engine, I assume the engine has a charging alternator, use the boat and the battery will stay charged for longer than you will need it to. Forget it, it's not a problem.
 
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