One more battery rabbit hole

[wincrasher]

I was looking in my WGO manual for something and came across this brief passage:

"If a battery does not contain at least 80%
charge during freezing temperatures, the
electrolyte can freeze and crack the battery case."

I had not heard (or noticed, I guess) this before. I always assumed that AGM batteries were good down to very low temperatures. I don't really see how someone who is running a furnace all nite, could keep the SOC above 80% to prevent damage.

[booster]

There is a chart in this link that shows the freezing temps at charge %. I didn't know it varied that much either.

charging AGM batteries in cold climates - northernarizona-windandsun

[wincrasher]

That's an interesting chart. So not as dire as someone would assume from the WGO manual.

[Boxster1971]

The Lifeline Technical Manual has a similar table for their AGM batteries that says they can withstand even lower temps. Copy attached.

[mkguitar]

if storing for the winter season, a good idea to remove batteries anyway.

if the vehicle is used fairly often, it should be at a good state of charge.

even in the cold CDN Prairies, I have never had a battery freeze and crack...I've had them not work well and at -50ºF had tires loose the bead overnight...but not a cracked casing

mike

[wincrasher]

My query was more about when using the van, not storing it.

Perfect example is what we had last nite - went from 40's during the day down to 15 overnight. We weren't expecting it to get that cold. If the power went out, we could have been down to 50% on the batteries from the furnace blower and other things running. Based on these charts there really wasn't anything to worry about, unless you didn't know anything and were relying on the WGO manual.

[eric1514]

Originally Posted by mkguitar

if storing for the winter season, a good idea to remove batteries anyway...

mike

Why? Those two charts prove a decently, not even fully charged battery will withstand hell freezing over.

[mkguitar]

a battery will last longer if stored indoors.

if in the vehicle, it may be subject to parasitic drain...radio memory, alarm and even electrons moving through dirt and moisture on the outside of the casing between the poles.

if a trickle charger/tender is used on a lead acid, then there may be a constant release of hydrogen gas and the battery will be constantly working undergoing a chemical process rather than "asleep". the plates will sulphate and water losses may kill the battery unless someone is checking and topping up

mike

[eric1514]

Originally Posted by mkguitar

a battery will last longer if stored indoors.

if in the vehicle, it may be subject to parasitic drain...radio memory, alarm and even electrons moving through dirt and moisture on the outside of the casing between the poles.

if a trickle charger/tender is used on a lead acid, then there may be a constant release of hydrogen gas and the battery will be constantly working undergoing a chemical process rather than "asleep". the plates will sulphate and water losses may kill the battery unless someone is checking and topping up

mike

Nah. I'll bet the battery in my constantly plugged in coach with it's 4 stage PD converter and sitting outdoors will be in better shape come spring than a battery that's removed and left alone indoors in a garage, heated or not.

[avanti]

I agree that there is no reason to store a fully-charged battery indoors. A complete battery disconnect switch is sufficient. I have left batteries out for many months under all kinds of conditions. Flip on the switch and the vehicle starts right up--every time.

[mlts22]

If the Travato has access to power, I'd just leave it plugged in and trickle charging off the converter all winter. I -think- Winnebago has a multi-stage charger that can float/maintain a 99%-100% SoC. If not, I'd just plug in a Battery Minder and let that keep things topped off. I'd actually consider two... one for the engine battery, one for the house bank.

[mkguitar]

Originally Posted by mlts22

...I'd just leave it plugged in and trickle charging off the converter all winter...

An owner can do that, but through all that time the battery will be constantly going through constant chemical processes releasing & recharging energy.

there is a cost to this

for me, it is worthwhile to take the time and pull a battery from a stored vehicle.
stored meaning months, not weeks.


Mike

[markopolo]

I'm in the keep it plugged in when not in use group. It seems to be working out really well 3.5 years later but I'll know better in a few more years.

The PD charger in my van will boost to 14.4 volts DC for 15 minutes every 21 hours so it's a bit different than just leaving the batteries on a battery minder for months.

[booster]

I have been sporadically looking at the issue of what is the best way to store batteries in off season for a couple of years, and all I have really learned is that there is not much for useful information to be had. Based on that, my guess would be that there isn't a big difference between methods. As long as the float voltage is low enough, you don't hear much of problems except if folks forget to water the wet cells or equipment messes up.

One of the things I did lately was test to see how much current our new Lifelines take on float, and it is tiny at only .1-.2 amps for 440ah at 13.2v float. I turned it up to 13.5v and the amps went up to about .5 and stayed there. I dropped the voltage to 13.0v and at first there was no current, but after a few weeks it was again in the .1-.2 amp range. The very interesting coincidence with all this is that the fresh off the charger, rested for 48 hours, voltage of the batteries is also right at the 13.2 volts. It appears that Lifeline has the float voltage set right at the very full rested voltage of the batteries and that is where they hit the lowest float current. Very interesting indeed, but if accurate it also makes it pretty easy to determine if you are at the correct float voltage just by testing rested voltage (but you have to be totally fully charged). Many other brands of AGMs give a higher than 13.2 volt float, so it would be interesting to see what their full rested voltage would be, and how much current they took compared to lower.

I mention this because I found several tech papers that talked about the recombinant efficiency not being 100% in AGMs. From this, I would conclude that whenever you are charging the battery, you are losing some amount of water and drying out the battery. On float, you have a current, so keeping it smaller seems like a good idea. The question I couldn't find an answer to is if float amps in an AGM are causing gassing (like they do in a wet cell to some degree) or just generating heat. If it is just heat, you wouldn't be drying out, but if it gassing you would be.

To further complicate it, AGMs that are designed for backup power supplies are made differently, it appears, to tolerate being full and on charge all the time. What is different and how much more vulnerable cycling batteries are is never discussed, that I have seen.

Many chargers now offer different profiles that probably were made to address this stuff. The Magnum we got has several different finishing modes. It can go to continuous float, shut off and go back to float when voltage drops to a setpoint, just shut off and stay off, shut off and run a complete charge cycle at a set voltage. In the recommendations they say to use the normal full time float only if you have loads running when charging, like when camping on shore power. Other than that, it appeared they prefer the shutoff and back to float or back to a full charge cycle. Personally, I would only use the full charge cycle if it were a return amp charge control so you wouldn't overcharge, as timers would almost surely overcharge.

I think that for us, in storage, we will use the shutoff and do a recharge cycle at maybe 12.8 volts. The batteries will take nearly 2 months to get to the 12.8 volts, unless the charger monitoring the voltage brings it down faster, so it will be a rare charge cycle run. I have simulated it on the bench by running the batteries down to 12.8v and running a charge cycle and it takes very little time, under an hour, to get to return amps and shut off.

Even though I have no good data to back it up, it just seems that putting a continuous .2 amps into AGMs, when they stay full for months anyway isn't all that great an idea. That works out to 5ah per day, 150ah per month, so it is a reasonable amount of charge (if it is really charge). The recharge at 12.8v only will put in about 20ah to be totally full, or about 7% of continuous float.

Again, I don't think any of this will make a major difference in life of batteries, but it may make some. Running them dead once will do much more harm that doing all this perfectly will save, I would bet.

With wet cells, I think I would use a low float voltage all the time, staying under gassing conditions. Being able to replenish the water is a big plus, and they need to be active.

This is a very interesting discussion. It is too bad you would be broke and dead long before you could ever conduct enough side by side testing to actually prove anything

[markopolo]

I realize now that Wincrasher was asking about the effect of low temperatures on batteries that are in use.

I never though about that. All of my really cold outside overnights have been with the RV plugged in.

A larger battery bank would be useful. A furnace & lights etc. wouldn't draw a good sized battery bank down.

Lead acid batteries might generate heat when being discharged. I haven't looked into it.

[avanti]

Here's an interesting chart:

battery temp.jpg

Source:

Battery Performance Characteristics - How to specify and test a battery

This reference says that batteries produce heat ("Joule heating") both when being charged and when being discharged, due to losses attributable to internal resistance.

They go on to say that the chemical processes in a given battery may be exothermic or endothermic.

[obgraham]

I think there is often a difference between theory and practice in this battery issue.

On me previous Winnie Journey, I left it plugged in, stored in my unheated shed over the winter. 3-stage charger supposedly, and a Trik-L-Start installed on the chassis. On return in the spring, the chassis batteries were dead, and the house batteries were way down on electrolyte, no doubt boiled off.

Obviously, something didn't work the way it was supposed to, probably the charger. But my batteries were shot anyway. After that, I would try like heck to plug in only 48 hours, every 2-4 weeks if possible, if the rig was sitting.

[booster]

With our wet cells, we found that they would be needing water about 1/2 way through the winter when on float, and the van is stored inside where it is warm. It was odd that the 12v Trojan deep cycles used much more water than the GC2 Trojans on the same 13.2 volts. I would think most any wet cell on float all winter would wind up low on water.

Folks that remove the batteries also need to remember that they will need to be charged over the winter a couple of times to do it right. Wet cells go down quickly sitting, AGM much more slowly. Lifeline says to charge a stored battery after 90 days of when it hits 12.5 volts which I think is about 75% SOC.

[avanti]

Originally Posted by booster

Folks that remove the batteries also need to remember that they will need to be charged over the winter a couple of times to do it right. Wet cells go down quickly sitting, AGM much more slowly.

Well, FWIW I have significant experience leaving automobiles unattended for long periods of time (typically 3-4 months, sometimes longer). I have battery disconnect switches, but I always leave them in the vehicles--summer and winter. Although I have not been measuring voltages, I can report that I have NEVER detected the slightest hesitation starting the vehicles after such interludes. This experience extends over several vehicles and almost 10 years.

For this reason, I am of the "disconnect and forget" persuasion. That said, on vehicles with solar, I don't even disconnect. That works too.

[markopolo]

Batteries are either being charged or they are discharging. It's one or the other. Self discharge is slow but it is still discharge.

Battery Sulfation : Technical Support Desk