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Old 12-10-2017, 09:12   #1
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Long Term Battery Storage

Need advice on storing AGM and wet cell batteries on my boat for periods up to a year, under the condition that nobody is available to do any monitoring or corrective action and only solar power is available and there are no cold temperature issues.

My understanding is that either type of lead acid battery should be provided with a current source of about 2% of its capacity in AH.with a peak voltage not to exceed about 14.4V, commonly referred to as float condition. Since no AC power was available, what i did was to connect one solar panel and set it at an angle at which it only produced 2A max. Figured this will keep my 400AH house bank peaked up since there are no loads. AGM of course requires no water to be added. But I may like to convert to wet cell in future. How do you folks using wet cell deal with such long term unattended storage requirements w.r.t. keeping up correct electrolyte levels?
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Old 12-10-2017, 10:20   #2
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Re: Long Term Battery Storage

I had my boat in dry storage for many years, and I had four regulated solar panels that kept the batteries charged. They were deep cycle gel batteries. Every year when I inspected the boat, I would flip on a manual bilge pump switch on the electrical panel, and the bilge pump instantly springs to life.

I am replacing the batteries during my refit, but I was impressed that solar panels can keep batteries functional for a very long time.
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Old 12-10-2017, 10:27   #3
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Re: Long Term Battery Storage

The name of the game with wet cells is to leave a tiny solar charge on them to prevent sulfation. A five watt panel will do the job and doesn't even need to be regulated. You fully charge the batteries when you get back to the boat and deal with electrolyte at that time.


*Edit to add: I've been doing this successfully through mid Atlantic winters for years with no issues.
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Old 12-10-2017, 12:48   #4
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Re: Long Term Battery Storage

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Originally Posted by waterman46 View Post
Need advice on storing AGM and wet cell batteries on my boat for periods up to a year, under the condition that nobody is available to do any monitoring or corrective action and only solar power is available and there are no cold temperature issues.

AGMs are supposed to have a very low self-discharge rate... and I've read that fully-charged AGMs can survive for longer than 1 year.

I've purposefully left our Odysseys to fend for themselves -- starting with fully charged batteries -- but only for about 5 months total. IIRC, they still measured about 12.6V when we started Spring commissioning the following year. This over a winter where freezing temps were normal in January and February, and it just varying degrees (pun) of "cold" in the latter half of Nov, all of Dec and Mar, and part of Apr.

-Chris
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Old 12-10-2017, 13:02   #5
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Re: Long Term Battery Storage

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Originally Posted by waterman46 View Post
>>>>>>>>>>>>>
>>>>>>>>>>>>>>>with a peak voltage not to exceed about 14.4V, commonly referred to as float condition. >>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
No it is not. Float is between 13.2 & 13.6.

Get your solar panel hooked to a controller. Don't depend on the tilt to control anything.
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Old 12-10-2017, 13:06   #6
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Re: Long Term Battery Storage

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Originally Posted by Drew13440 View Post
The name of the game with wet cells is to leave a tiny solar charge on them to prevent sulfation. A five watt panel will do the job and doesn't even need to be regulated. You fully charge the batteries when you get back to the boat and deal with electrolyte at that time.


*Edit to add: I've been doing this successfully through mid Atlantic winters for years with no issues.
While I respect your success over the years, it would be unwise to connect a solar panel without a controller.

From Maine Sail's small solar panel install on his website:

Installing A Small Marine Solar System Photo Gallery by Compass Marine How To at pbase.com

Do I Need A Controller ?
I get asked this question quite often and the answer is almost always a resounding yes.


In this photo I have two group 27 batteries, in parallel, consisting of 160 Ah's at the 20 hour rate. The batteries were fully charged then went into float mode.


As we can see on the digital volt meter the current accepted / needed to maintain a float condition, on these two parallel group 27 batteries, is just 0.08A or eight one hundredths of an amp. EIGHT HUNDREDTHS OF AN AMP!


A rather diminutive 10W panel can produce about 0.51A. Even with a small panel if the bank is left on charge for multiple days at a time, with no loads as is the case with many boats, you can over charge your batteries. While that difference may not sound like much the difference between the 0.08A the batteries want to accept at float voltage and what a 10W panel can produce, about 0.51A, is a 537% increase in current.
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Old 13-10-2017, 09:14   #7
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Re: Long Term Battery Storage

We leave our boat for 6+ months each season. Our house bank, 6 Trogen T-105s, are wet but with moisture control caps on ea cell, and we have 4-80watt solar panels that feed a a solar controller permanently installed. We turn off all DC electric-except the bilge pumps. We've found that it's best to disconnect 3 of the 4 panels, and just leave 1 panel feeding the controller to maintain the house bank during our absence. It's worked well now for the past 3 seasons, and when we return the batts are fully charged, the electrolyte level is OK, and the bilge is dry.... even though we "summer over" in Puerto Rico (with heavy rains and hurricane potential).
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Old 13-10-2017, 10:10   #8
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Re: Long Term Battery Storage

AGM float is ~13.6V and varies with temperature. Keep the controller charge at or below float. The AGM's usually have gas recirculation so no need to worry about water loss.

Most electronics (solar controllers, clocks, battery monitors, some auto bilge switches) have a quiescent current drain which may be very small but significant over time. Disconnect them unless in use.

If you are using a battery diode isolator between battery banks, be sure not to connect the isolator to a bad, old, or failing bank. They won't drain the other banks, but they might have so much current draw that they lower the available charging voltage for all banks. If you use a solar controller with a battery isolator to charge multiple banks, make sure the controller has a battery voltage sense wire and associated sense circuit that is directly connected to one bank. The sense wire looks at the actual voltage on the battery side of the diode isolator and ensures the proper charging voltage.
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Old 13-10-2017, 10:44   #9
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Re: Long Term Battery Storage

Quote:
Originally Posted by Stu Jackson View Post
While I respect your success over the years, it would be unwise to connect a solar panel without a controller.

From Maine Sail's small solar panel install on his website:

Installing A Small Marine Solar System Photo Gallery by Compass Marine How To at pbase.com

Do I Need A Controller ?
I get asked this question quite often and the answer is almost always a resounding yes.


In this photo I have two group 27 batteries, in parallel, consisting of 160 Ah's at the 20 hour rate. The batteries were fully charged then went into float mode.


As we can see on the digital volt meter the current accepted / needed to maintain a float condition, on these two parallel group 27 batteries, is just 0.08A or eight one hundredths of an amp. EIGHT HUNDREDTHS OF AN AMP!


A rather diminutive 10W panel can produce about 0.51A. Even with a small panel if the bank is left on charge for multiple days at a time, with no loads as is the case with many boats, you can over charge your batteries. While that difference may not sound like much the difference between the 0.08A the batteries want to accept at float voltage and what a 10W panel can produce, about 0.51A, is a 537% increase in current.
Fair enough, but Maine Sail's bank is fully charged when put away. Mine is not. A five watt panel is capable of .3 amps in direct sunlight, which it never gets during winter layup. Maybe it gets five hours per day at a thirty degree angle? That is probably good for .5 to .75 Ah per day, an amount that would be given back over night.

Anyway, my point was that sulfation is what will kill an unused wet cell. All that is needed is the slightest electrical charge every 24 hours to prevent it.
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Old 13-10-2017, 11:13   #10
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Re: Long Term Battery Storage

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Originally Posted by Drew13440 View Post
Fair enough, but Maine Sail's bank is fully charged when put away. Mine is not. A five watt panel is capable of .3 amps in direct sunlight, which it never gets during winter layup. Maybe it gets five hours per day at a thirty degree angle? That is probably good for .5 to .75 Ah per day, an amount that would be given back over night.

Anyway, my point was that sulfation is what will kill an unused wet cell. All that is needed is the slightest electrical charge every 24 hours to prevent it.
It's not the amps but the volts that'll getcha.

Your boat, your choice.

I tried.

I bought a $22 controller when I left my boat for all of a month in 2016. No damage from an 11 W panel laid in the cockpit, 390 ah house bank, wet cells. $22!!! Sheez...What's your whole bank worth?
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Old 13-10-2017, 14:34   #11
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Re: Long Term Battery Storage

I have a question on this relevant topic. My boat is stored inside a Quonset with a somewhat translucent "roof". It is moderately bright inside there. Every year the marina disconnects my house and start battery and that is it. I make sure they are fully charged at the outset. All has been well.

New this season - 2 golf cart batteries for house, and a new 265W solar panel keeping them fully up (while at the dock). There will be no draw whatsoever over the winter while inside.

My thinking is to tell the marina to leave the batteries hooked up - of course, they are protected by an ACR and 30A MPPT controller. I think the muted daylight inside the storage building will keep the batteries charged and safe. Comments?

Now, otoh if the boat ends up in the older wooden shed, I will have them unhook the battery cables since there will not be sufficient light to stimulate the solar panel.
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Old 13-10-2017, 19:18   #12
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Re: Long Term Battery Storage

Whatever you fo with there is always the possibility of a system failure. This can lead to some nasty runaway incidents. Possibly just loosing the battery but also possibly a fire. If you possibly can have someone inspect the boat once a month to check voltages and electrolytes. I speak from fairly bitter experience!!
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Old 14-10-2017, 07:43   #13
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Re: Long Term Battery Storage

In my original post I did make an error. Thanks Stu for correcting me that float voltage should have been given as around 13.2 to 13.6. I was thinking of the max voltage for absorption mode.

Bottom line Ive been able to get from all the replies is that a quite small solar panel with a good charge controller and moisture control caps, if wetcell, should be ok without supervision for some number of months.

Doug
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