New Portable Battery Charger for Winter Storage

[Nichole340]

I want to buy a new battery charger for the garage and use it maintain my boat batteries over the winter. My battery tender is not up to the job.
I want the Victron Blue Series of chargers but not sure of the best for my needs.
I have 2 - 6 Volt Duracell GC2 230 AH and 1 - 12 Volt Duracell Group 31 Batteries.
What are others using at your house during the winter? Do you charge your 6 Volt batteries separately or together as one 12 volt bank (as on the boat)?
Looking forward to reading your suggestions and advise as always.

 

[JoeWhite]

I would remove the shorepower charger from the boat and take it home to charge the batteries.

 

[Davidasailor26]

Curious about how the tender is not up to the job, and if any charger is really needed at all. My preference is to just disconnect the batteries and leave them in place. In cold winters the self-discharge is very slow, to the point where there could be more risk relying on power and a charger than just letting them sit. Here’s Maine Sail’s article on the topic - Winter Battery Storage & Self Discharge Characteristics - Marine How To

 

[Don S/V ILLusion]

Never bothered removing the batteries when it was in RI. Typical self-discharge rate in cool/cold weather is minimal as long as you disconnect them to ensure no parasitic loads. Just make sure they are fully charged before abandoning them for winter

 

[jssailem]

Looking forward to reading your suggestions and advise as always.

Read the "Marine How To" article posted by @Davidasailor26
One of the best available.

 

[dlochner]

Make certain the batteries are fully watered and fully charged. Disconnect the negative cable and leave them till spring. Charge them the first opportunity you get when the boat is uncovered. They will be fine.

 

[Nichole340]

Well, my battery tender never stops showing me the red light, regardless of any battery I use it on. So its toast.
I haven’t removed the batteries from the boat just yet, I need a good charger for my other batteries at home and thought why not get one for the boat as well.
Right now they are fully charged and disconnected from the boat and each other. I was planning on taking them off the boat this week, but now I am rethinking that idea as unnecessary, given all your advise and links.
Thank you all again.

 

[dlochner]

Battery chargers should be sized based on the size and type of battery, FLA, AGM, LFP. Each battery type and manufacturer has an optimal charging voltage. You have FLA batteries which are pretty forgiving.

FLA batteries can generally accept between 10% and 20% of their capacity (usually presented as .1C to .2C). The largest bank you have is the 2 GC with 230ah, thus they would like to have around 20 - 40amps of charging current. The Group 31 has about 100ah so it would want 10 to 20 amps of charging current.

So, to answer your question, a charger in the 20 -30 amp range is probably the best bet. It will be a little oversized for the Group 31 and in the middle of the range for the GCs. It is probably better to have the charging current a little higher than lower for an FLA battery because as the battery charges the internal resistance increases the current it can accept will be lower.

 

[Rich Stidger]

In addition to disconnecting one of the battery connections, also make sure that the tops of the battery and the terminals are scrupulously clean and free from any electrolyte. Wiping with a rag soaked in water with baking soda is a good cleaner. But do it with the cell caps on so that none of the baking soda solution gets into the cells.

 

[Ward H]

I'm another that simply ensures the batteries are full of water and fully charged. Then disconnect them until spring. They have held 12.7v thru 5 winters.

 

[High Current]

Piling onto the “just disconnect them” sentiment but with additional details.

Keep an eye on them. You want the voltage to stay above 6.2V (12.4V) to prevent sulfation. If they drop close to or below that threshold then a one-time top-off charge will suffice. I would feel better about that than leaving a charger on 24/7 (potential fire risk especially for cheaper ones).

I bring mine home since the boat is 200 miles away. I use a simple Harbor Freight charger to top them off.

Connecting two 6V in series to make 12V is fine - internally they’re already 3 cells in series. Just make sure they’re at reasonably matched state of charge first, otherwise the equalization charge will take forever and use up a lot of water.

 

[JBP-PA]

While I did not leave them sit all winter, I never used a battery tender either. I would top them up every couple months with an ordinary charger. I did not have 6V, but I assume you charge the 6V together on the boat, so why not do the same at home.

 

[SycloneDriver]

There is a lot of good advice above.

About "BatteryTender" I have had good luck with them at work on many portable generators. I have learned a few things though. The only unit that is temperature compendated is the "Plus." The new units seem to behave differently than units from a few years ago. They seem to float at a lower voltage or they go too sleep for some period of time, I think California law may have something to do with this.

I am trying out a small Victron unit on one of my generators and so far I like it, I'll know more in a few years.

 

[bawlmer]

Make certain the batteries are fully watered and fully charged. Disconnect the negative cable and leave them till spring. Charge them the first opportunity you get when the boat is uncovered. They will be fine.

^^^This^^^

 

[Ward H]

About "BatteryTender" I have had good luck with them at work on many portable generators.

Good info. Thanks

This raises a question I've thinking about.
I know batteries have a self discharge rate and in a colder environment the discharge rate is less than if in a hot environment.
I know myself and several others fully charge our batteries and disconnect them until next year.

If the battery self discharges say from 12.7 v to 12.2 v is that an indicator the battery is nearing end of life?
Does using a battery tender cover up this decline in a battery's health?
Does it really extend a battery's life or is it old school from the days when we put our flashlight batteries in the fridge until needed and heaven forbid we stored a car battery on concrete.

And it's not the same scenario as keeping a back up generator ready to start at any moment despite the health of the battery.

I misspoke earlier. My GC2 batteries have been stored fully charged and disconnect for 5 winter seasons except for year 2. I was having surgery and trusted a mechanic to disconnect them and he forgot I found them in the spring at 12.0 v.
Last season, the 5th, I found them at 12.6 v after 6 months.

The main reason I'm asking this question is I screwed up a few weeks back. I forgot to turn the charger back on after a day sail. I returned to the boat 2 weeks later to find the batteries at 5v. They charged back up and appear to be fine. I figure if they don't self discharge to a low voltage over the winter I didn't do any measurable harm to them.

 

[dlochner]

Good info. Thanks

This raises a question I've thinking about.
I know batteries have a self discharge rate and in a colder environment the discharge rate is less than if in a hot environment.
I know myself and several others fully charge our batteries and disconnect them until next year.

If the battery self discharges say from 12.7 v to 12.2 v is that an indicator the battery is nearing end of life?
Does using a battery tender cover up this decline in a battery's health?
Does it really extend a battery's life or is it old school from the days when we put our flashlight batteries in the fridge until needed and heaven forbid we stored a car battery on concrete.

And it's not the same scenario as keeping a back up generator ready to start at any moment despite the health of the battery.

I misspoke earlier. My GC2 batteries have been stored fully charged and disconnect for 5 winter seasons except for year 2. I was having surgery and trusted a mechanic to disconnect them and he forgot I found them in the spring at 12.0 v.
Last season, the 5th, I found them at 12.6 v after 6 months.

The main reason I'm asking this question is I screwed up a few weeks back. I forgot to turn the charger back on after a day sail. I returned to the boat 2 weeks later to find the batteries at 5v. They charged back up and appear to be fine. I figure if they don't self discharge to a low voltage over the winter I didn't do any measurable harm to them.

The 50% discharge guideline is a guideline, not a death sentence. Most batteries are robust enough to survive a couple of very deep discharges without major damage. However, each deep discharge does some damage and the damage is cumulative. I had a set of 6v GCs that were accidentally deeply discharged when I left for a couple of days with the refrigerator on and the battery charger off. They were still working well 5 years later when I replaced them. Had the batteries been several years older, the results might not have been the same.

 

[dLj]

Given the fact you are looking for a house charging system, might have batteries that could need a solid equalization cycle, and aren't going to use it on the boat, I'd suggest getting a power supply with programable voltage and current so that you would be able to run equalization cycles that are specific to the battery you are working with.

As others have said, you don't need to run a float charge over the winter if the battery is sitting dormant. But you may be better served having the ability to run equalization cycles as needed.

dj

 

[sailme88]

Charges tend to cook batteries....you want that tender... if the one you have is too small, upgrade it.