Lithium batts: How to heat in cold condx?

[svbravo]

Currently building new aluminum boat. The hull is insulated above the waterline, but the battery compartment is below, under the floorboards. House battery bank will be LiFePO4. The boat will be used in high latitudes, where water temp is frequently near freezing temps. We know that the lithium batts do not like charging when cold.....in fact, Victron and likely others void their warranty if charging below 5 deg C.

I've been thinking of insulating the battery compartment from the hull. Not too big a deal w/ closed cell foam. Wondering how to keep the compartment warm...we will have a Refleks heater w/ glycol loop aboard, so possibly running the warm hose through the compartment would work. Also considering one of the silicone rubber industrial heating pads. They're available in 12V, but use a lot of electricity.

Has anyone else dealt with this issue, and come up with any creative ideas for keeping the battery compartment warm???

[Lepke]

If you box your batteries in with thick styrofoam panels or spray in foam, you don't need much heat. Maybe one of those tapes that wrap pipes. I have my water heater boxed in with 2" styrofoam and it holds heat for more than 2 days in cold weather.
I don't know much about lithium batteries, but would guess if they are being charged, that would create some heat. My mother-in-law took lithium, but she got it from a pharmacy.

[Checkswrecks]

First off, if the battery is disconnected, Li-ion will stayed charged for years if there aren't parasitic drains for clocks, alarms, bilge pumps, etc.

Lithium batteries generate their own heat internally with discharge, such as turning on a car headlight. This is not practical for a battery in storage. If the battery does have parasitic discharges, then it needs a charger to occasionally function. For them to say 5 Celsius (41F) is conservative on the manufacturer's part. As long as you are not hitting it with a high charge rate, you could go to freezing.

Two things to avoid are uneven heating, such as putting a heat pad on a side, and overheating.

Here's an example of a low watt heater and it ought to put out enough heat for the entire compartment to stay above 5C. Again, don't put the heat close to one side of the battery.
https://www.amazon.com/dp/B004Q0LG4E...d-7fcf5515c0e8

If the compartment still gets below freezing then lining it with the pink foam boards would be quick and easy. If you do try this, stick in a meat thermometer and check it for a long period of time to make sure the temp doesn't get too high. With enough time, those little goldenrods can heat an entire small gun safe hotter than you want your battery.
https://c1.staticflickr.com/3/2459/3...5eb5b383_b.jpg

[john61ct]

Flexible silicon heating pads are cheap, even custom made to your specs with a thermostat cutoff built in. From China obviously, search eBay.

The key is never allow **charging** while freezing, can mean instant scrap.

[cj88]

Any reason they can't extend the spray cork and foam insulation into that area?

[john61ct]

"They" who?

So few boaters are using LFP not worth the boat makers' while, up to the owner to get that done.

Of course if living in arctic conditions the whole living space should really be well insulated, but that's hard to retrofit.

[CatNewBee]

are you staying in sub zero conditions in the water?

You can use LiFeYPO4 batteries, range -40 ... 60°C, if you have them installed in the living area, they will be warm anyway. More of a problem is keeping the batteries cool in the tropic waters, they degrade from heat more than from cold conditions.

[john61ct]

You really believe that claim, can charge at -40° ?

I believe Maine Sail's expressed great skepticism about that, I inferred Mr Winston maybe not such a straight shooter?

[CatNewBee]

Originally Posted by john61ct

You really believe that claim, can charge at -40° ?

I believe Maine Sail's expressed great skepticism about that, I inferred Mr Winston maybe not such a straight shooter?

you can charge them with a reduced current, not 1C, but yes, it works. You can discharge LFP in sub zero anyway, of course you have less usable capacity when it's cold.

[Checkswrecks]

Heat pads work best in contact, which is what you do not want. Inside the battery, the foils on the side with the warmth will work harder than the colder side simply because electrons are lazy and go where it is easiest. The one side will then age faster and develop higher resistance, which becomes a compounding problem as the electrons migrate toward the side with lower resistance. In short, the cell goes to an early lack of capacity and early death.

Cold charging generates a different internal problem electro-chemically, also resulting in early failure. It's not hard for the manufacturer's lab to tell how the battery died. Technically you could cold charge down to the roughly -20 area without harm, especially at 1C, but why challenge things when prevention and retaining your warranty is not that hard?


(fwiw, I'm intentionally trying to keep this explanation at a non-geek level. I've been working with Li-ion battery failures for years and been at the factories. It's easy to get into the weeds fast.)

[Hunky Dory]

In Canada most people use a plug in low wattage battery blanket heater with a built in thermostat for vehicles, We are presently going through the coldest February in over 20 years, high temp during the day is -25-30C . These pads are premade with a vinyl cover, built in insulation and a short power cord, Just wrap around the battery and plug in. The cost is around $15. Cdn.

[john61ct]

Yes if you have mains available no challenge at all.

That comes when living off grid, and the power for warming the bank must come from the bank, before you can start charging it.

[DeepFrz]

If you run the return line of your water heater into the battery compartment and make a couple of loops around the bottom of the batteries it should warm the batteries but I think you should have a thermostatically controlled bypass installed.

[svbravo]

It does sound like most agree that charging when ambient temp of the battery enclosure (below the floor in the keel) when near freezing is a definite issue. My plan at this point is to insulate the space just like the rest of the living spaces above the floor. Could either be done by manuf (preferable) or me after delivery.

Then for a heat source, I’m leaning toward a simple 12v in-line blower, ducted between the salon and the battery space immediately beneath it. That should keep the batts at close to cabin temp, without the energy drain of another heat source. Could control with a simple thermostat. Will also put a remote temp sensor in the batt bank to monitor.

Thanks for all the input. Though I’ve been happily running our current boat on lithium’s for past 3 years since designing and installing the 600Ah bank, this cold weather charging issue is new for me.

[nwdiver]

Running your heating line through will work I run mine under the flooring instead of behind the furniture and it warms it up and keeps the bilge dry.......