Batteries left on Boat Through the Maine Winter

[Plumbean]

I have AGMs on board, set up with a start bank and a house bank. I have always left them on board for the winter. One question for the hive mind about the requirement to disconnect all the negative leads. In my set up, I have a battery switch for each bank that is up stream of all loads on the system. This setup allows me to utilize the Dual Circuit Plus main battery switch and still isolate a bad battery bank if need be. As a result I can completely isolate both banks for the winter from all loads on the system. Is there any benefit to also disconnecting the leads in this case? I would think not since the banks are completely isolated and it is much easier to just flip the switches for the winter. But it does mean that the AGMs in my house bank are connected to each other.

[noelex 77]

In colder temperatures lead acid battery have a low enough self discharge that they will be OK provided there is no parasitic drain over the winter period. However, this is not ideal, especially for older batteries. It is healthier to keep them at or close to 100% SOC without overcharging. This will produce the least degradation in storage.

To achieve this, you need a charge source that can be programmed with storage voltage set points. These are typically around 0.5-0.6V lower than the float voltage at around 13.2V. Most Victron gear (MPPT solar controllers and battery chargers) will do this; some will even automatically select the appropriate storage voltage set points.

The other difficulty is finding a reliable source of power (solar or shore power). It is important that it continues to function. If shore power is unplugged or the solar panels become covered in snow, there will often be some parasitic drain from the connected devices, which can drive the SOC to damaging levels.

As mains power is excluded in your case, the only option is solar. It only needs a small panel, but if there is a danger that this will be covered in snow for long periods, it would be better to disconnect the batteries completely.

[epoxyman]

Based on the input from everyone, I am going to do the following:
1) When the sailboat is laid up I will top off electrolyte and verify full charge
2) Until it gets really cold (below freezing) I will use my Victron data feed to track the state of charge of my batteries, and disconnect the negative leads from the system but leave them connected in parallel to the other batteries so that the solar panel keeps the charge.
3) Once the dead of winter sets in, every couple of weeks show up with my Honda 2000 and connect as shore power to charge the batteries for a couple of hours using my inverter and on board battery charging system.
4) Keep an eye on the SOC for all 5 group 24 lead acid batteries to verify that they are maintaining an above 12.4V charge.

Please if anyone sees a problem with this plan - SCREAM at me

[Mike OReilly]

Your plan is overkill, but certain to leave your batteries as good as they can be.

[CarlF]

Since your batteries are just regular deep cycle (not Trojan or other super premium brand), I would just plan to replace them in the spring when it's easy to get the yard to help you lift them. Seven years is above average. My boat builder friend always recommends replacing at 5 years to never loose a week of sailing to battery problems in the middle of the short NE cruising season.

And I would at least consider swithing to lithium. Lithium cost per year is now much cheaper than lead. And every motor on the boat runs better at lithium's 13v than lead's 12.5v resting voltage. The necessary changes to the electrical system are now well understood and not difficult in most cases.

[gulfislandfred]

Interstate batteries are remarkably long lived.
The company is also very responsive.
Call or contact tech support at their head office, and ask your question.

[blackbjo]

Hi

Echo many of the comments above about leaving batteries on the boat but fully disconnected. We have done this for the last 5 years - 4 AGM 100aH house I used to measure them at start and end of winter and voltage drop wa less than 0.5v. Boat lives up in Lake Superior - so I would say colder than Maine

The issue with leaving anything connected at all is that whatever it is - even solar charge controller - takes some current. If something goes wrong - eg solar panel breaks/dies then the battery will slowly be sucked down.

I have Victron battery sense monitors on some batteries - eg bow thruster - they come off as well. I actually remove both positive and negative of every battery - I do not trust the switches. Yes I know that is over the top - but is more about making sure I do not miss something.

Reds

John

[Tanqueray]

Originally Posted by epoxyman

Based on the input from everyone, I am going to do the following:
1) When the sailboat is laid up I will top off electrolyte and verify full charge
2) Until it gets really cold (below freezing) I will use my Victron data feed to track the state of charge of my batteries, and disconnect the negative leads from the system but leave them connected in parallel to the other batteries so that the solar panel keeps the charge.
3) Once the dead of winter sets in, every couple of weeks show up with my Honda 2000 and connect as shore power to charge the batteries for a couple of hours using my inverter and on board battery charging system.
4) Keep an eye on the SOC for all 5 group 24 lead acid batteries to verify that they are maintaining an above 12.4V charge.

Please if anyone sees a problem with this plan - SCREAM at me

I would say overkill, especially for older batteries. No reason to sacrifice them yet, but charging for several hours a month is probably not required. But you have obviously taken good care if them…so no worries.

I am in Chicago, and it gets cold here too. I leave my 6-volt go,f cart batteries on board, but disconnected. They have weathered ok.

I added a LFP house bank this year, and those will be removed for the winter and stored in my basement. But lead acid…stay on the boat.

Greg