Battery Advice For Overwinter

B

Besonders

Well-Known Member
Joined
1 Dec 2012
Messages
103
Location
Med for the summer, Caribbean for the winter
Visit site
I currently have 3 x 125AH leisure batteries which are charged via regulator by 2 x solar panels (1x 100w & 1x 35w). The boat is hauled and stored on the hard in Greece October to April each year. During the layup period the boat has no requirement for power. The boat has full covers and is always dry, if a little foisty but certainly no water ingress that may require the auto bilge pump. I am seeking advice on what is considered to be best practice to preserve the life of the batteries. Should I disconnect and cover both solar panels and remove the leads from the battery terminals or is it better to have some charge from say the smaller 35w panel to keep the batteries fully charged.
I understand batteries have a finite number of charging cycles and this is verses leaving the batteries to slowly discharge over a period of 6 - 7 months. I would appreciate opinions as to which is the most detrimental to overall battery life.
 
aquaplane said:
How much are 3 batteries going to cost you? Is it more than a flight or two to your boat?

Can't you leave your solar connected to keep your batteries in good condition?
Click to expand...

Bob, thanks for the reoly. Obviously I could leave them connected but I am asking the question is it better for overall battery life to do so given batteries have a limited number of charging cycles or is it better to 'give them a rest' for want of a better term or will that rest for 6 - 7 months be more detrimental as they will be slowly discharging
 
Leave the panels connect and the loads turned off. X cycles is discharged and recharged x times. The more the discharge, the worse for the battery.
 
It is a dilemma, and one I'll be facing soon. As said, charging cycles is not really an issue, since they won't be cycling: they'll either be kept topped-up, or slowly self-discharge, depending which option you adopt. But lead-acid batteries are certainly best maintained at full charge.

Self-discharge varies with battery type, generally being lower with lead-calcium than lead-antimony. You may be able to get manfacturer's data for yours on-line, but I wouldn't hold my breath. 5% per month is often suggested as a rule of thumb. Exide recommend that stored, disconnected lead-acid batteries should be first left at 100% charged and brought back to full charge every six months (a time which shortens dramatically with temperatures substantially above 25C, which shouldn't be an issue).

I have an innate reluctance to leave things switched on during extended absences, and would prefer to disconnect the batteries altogether. It may well be that just leaving the 35W panel to do its stuff, as you've considered, would work. Even if the regulator were to fail in a way that left it connected to the batteries, it's only going to be putting in a couple of amps during the winter, which shouldn't unduly worry a 375Ah bank. Yet that will be more than enough to overcome their self-discharge. No doubt someone will be along with wise words.

Any better informed suggestions, I'm all ears.
 
Last edited:
In exactly the same situation as the OP I have tried both approaches. In the past I left a 38 watt solar panel connected via my regulator but that panel now seems to be dead. Last year I left the full 125 watts of panels connected. The previous year I disconnected all batteries from each other. In every case the batteries were perfectly charged when I returned to the boat. Even after six months the disconnected batteries had 12.6 volts in them and were working fine. The panel charged ones were up to 13 volts but there is a risk that they could lose water excessively, in which case disconnecting them all seems to be the better choice.
 
vyv_cox said:
The panel charged ones were up to 13 volts but there is a risk that they could lose water excessively, in which case disconnecting them all seems to be the better choice.
Click to expand...

I was planning to leave my new sealed lead acid batteries in place over winter (a 270ah bank and a Red Flash 1100 with a 30 watt panel and regulator feeding both batteries) keeping them topped up, assuming that 13 volts would not cause water loss. It sounds like you think this is a bad idea ... I thought they were safe enough below 14 volts. No?
 
Last edited:
My boat had new domestic batteries fitted in 2013 by the previous owner. The boat was then not used much, if at all. The 120w solar panels were left on all of the time, even when the boat was de-commisioned and put up for sale, on the hard. The batteries were all fully charged when i bought her and had lost no water.

I think the only way any harm could come to the batteries would be if the controllers failed in a way that allow all of the current to reach the batteries. But if i was away from the boat for even a short time 120w of un-regulated solar panels won't be dong them any favours.
 
My system is to plug my Sterling 20A charger into shore power for 24 hours in December and again in April and my last set of batteries lasted 10 years. Isn't there someone in Greece who could do this for you?
 
The 35W panel on it's own through a regulator would be fine at keeping 400Ah topped up in the Med/Caribbean and almost no chance of over-charging so I would disconnect the 100W panel over the winter if that is easy. If disconnection is difficult I would leave the entire 135W connected. I have a 40W panel through a controller which keeps 800Ah topped up over winter and these batteries are over 8 years old and seem as good as when they were new.

Richard
 
You really need the specific storage instructions from the battery manufacturer but I have always taken the view that fully charged is better. AT best if disconnected they may self discharge and you then recharge them and have used 1 cycle.
AT worst - if you are delayed getting back they may fall below 50% charge and suffer serious damage. so why take the risk.

I would ensure all batteries are connected to the smaller panel with the controller in place. The usual advice seems to be a panel with a Wattage figure of 10% ( or less) of the battery Ah figure doesn't need a regulator. Whilst I wouldn't risk that approach myself it should give some confidence that even if the regulator fails the batteries will not be damaged.

Cover the other panel up completely and also physically disconnect it from the controller. that should also extend the life the solar panel as they seem to deteriorate with age / exposure to the elements,
 
Last winter I left my single 100ah battery connected to it's 30w panel using a simple switched type solar controller (not a PWM type ?)
This year I will do the same but I have since replaced the simple controller with a Victron MPPT type. This has a float mode which will operate I assume all winter.
 
My solars 2x80 stay connected all year but that's in uk. I would be very disappointed if any of the batteries (1x125 + 2×80) last less than 6 or 7 years.
Maybe where you are I might reduce the solar input a bit.
Re stated battery life discharge cycles, isn't that complete discharge / recharge cycles, so nothing to do with trickle charging to maintain a fully charged battery?
PS I also have 2x125 in series for 24v system which is charged via a WG which is always spinning when there is wind and those batteries also have good longevity.
 
When ashore, I have a Ctek 5amp charger which I connect to one battery for about 3/4 weeks then swop over to the 2nd battery. They certainly seem fine after 10yrs. although one did go flat once this year when on a weekly cruise, so maybe near the end of their life. 2 x 110ah leisure batteries.
I used to bring them home each winter and again used a Ctek maintenance charger but I'm finding they are a bit heavy nowadays!
 
If you want to shorten the life of your batteries, leave them disconnected for long periods.
They all suffer from self discharge so I would not leave my batteries for more than 30days.
A good mppt charge controller should float the batteries at around 13v which doesn't normally cause a problem. Cheap pwm controllers are probably a bad idea unless you reduce the number of solar panels or use a smaller one.
 
ianj99 said:
If you want to shorten the life of your batteries, leave them disconnected for long periods.
They all suffer from self discharge so I would not leave my batteries for more than 30days.
A good mppt charge controller should float the batteries at around 13v which doesn't normally cause a problem. Cheap pwm controllers are probably a bad idea unless you reduce the number of solar panels or use a smaller one.
Click to expand...

Some sort of float charger at about 13V to 13.5V would be ideal.
MPPT or PWM are not relevant to this.
MPPT is about extracting max power from the panel, PWM is a regulation method in a switch-mode voltage converter.
There are plenty of mains powered float chargers around, sold for motorbikes etc over the winter. Is there a solar equivalent? Other than float mode on a more powerful regulator.
I can understand the reluctance to leave a high power charger switched on, even if it is solar powered.
A small unregulated panel works well for winter in the UK, when the boat is used occasionally. Not sure it would be ideal for layup in Greece.
 
lw395 said:
Some sort of float charger at about 13V to 13.5V would be ideal.
MPPT or PWM are not relevant to this.
MPPT is about extracting max power from the panel, PWM is a regulation method in a switch-mode voltage converter.
.
Click to expand...

I should have added that the reason for recommending a mppt charge controller is they tend to be better at that job than the cheap Chinese pwm type supplied with panels, rather than because they are better at getting more from the panel. (although in a dull region like Scotland, every little helps, especially over the long winter days)
 
ianj99 said:
I should have added that the reason for recommending a mppt charge controller is they tend to be better at that job than the cheap Chinese pwm type supplied with panels, rather than because they are better at getting more from the panel. (although in a dull region like Scotland, every little helps, especially over the long winter days)
Click to expand...

OTOH a good quality PWM controller might be preferable to a cheap Chinese MPPT controller
 
For the past three winters I've turned off all the electrics in the boat but left the solar panels connected (100 watts of panels, 490 ah batteries via an mppt controller). The only problem I had was the first year where I forgot to leave the link to the starter battery switched on: it died but the house bank didn't. Since then I've come back to float charged batteries ready to leave the yard. That's in Greece but I'd do the same in U.K.
 
You must log in or register to reply here.

Share this page

Top