AGM temperature range

Horsefly

I just noticed that the manufacture specifies the following operating temperature ranges for my AGM batteries:

• Discharge: -4F to 140F
• Charge: 14F to 140F
• Storage: -4F to 140F

My system is at 9,000 ft elevation in Colorado, and it will probably be long periods this winter when the temp will certainly not get above 14F, and maybe not even above -4F. 

I was hoping to keep the charge controller on all winter, keeping the batteries mostly in float through the winter, except after snow has covered the panels for some number of days.

How much of a problem do I really have?  I've sent the question to the manufacturer as well, but I figured I could get some unbiased expertise here as well.

Estragon

I wonder if charging temp lower limit is because voltage might be too high (compensated).

The discharging/storage temps seem pretty conservative. A fully charged, or close to it, lead acid battery, (AGM or flooded) with typical SG electrolyte, won't freeze until much lower than -4°f. Lots of car batteries are AGMs, and we can go weeks under that around here. We might need a block heater to keep the oil from getting too viscous, but batteries work (with lower cranking amps).

Aside from just being conservative, the only reason I can think of for such high minimum temps is a low SG electrolyte.

I'd be interested to hear what the manufacturer has to say.

jonr

If you want to use the battery (vs idle), maybe you can stick them in a thick foam box and heat them to 14F.

BB.

Generally, it is not recommended to recharge a frozen lead acid battery (presumably of any type). Perhaps discharging a frozen battery is not a big issue.

Presumably, the numbers are based on the minimum rated state of charge of the battery/cell (i.e., low state of charge, battery will freeze at "less cold" temperatures). AGM are supposed to withstand some freezing, but I would not make a habit of it (most things do not do well when water/electrolyte freezes and thaws--Expansion and contraction).

If the batteries are not deeply cycled, then they will freeze at colder temperatures, and you can charge them at colder temperatures too (I am not a battery engineer).

-Bill

mvas

Generally, we do not heat batteries when they are "hibernating".
I would not waste any energy heating a cold AGM battery.
When they are fully charged, they can withstand very cold temperatures.
When they are cold, there is very little self-discharging.

Storage above -4F, is not realistic; Vmaxx needs to explain why.
Charge above 14F, is not realistic; Vmaxx needs to explain why.

Does the Vmaxx Charge Controller actually stop charging when the battery temp drops below 14F ?
Maybe, they they do not consider "Float" as a charging.mode - only Bulk & Absorb?

Lifeline AGM
==========
Storage = -67F
Charge = -40F

Horsefly

Thanks guys. I was busy driving back from the cabin. Still no word from Vmax. I tend to agree with that these temps must be on the conservative side, and maybe assuming the batteries are mostly discharged.  I may just send them the Lifeline info that @mvas posted and ask why their batteries would be so different. In my email I did explain that the batteries would be mostly in float all winter, so maybe they will give me a different set of temperatures for that situation.

My sister and brother-in-law, who have actually skied into the cabin in the winter a couple of times, think that we may still be OK. The batteries and the rest of the electronics are in the basement of the cabin, which is below grade. They put jugs of water down there just in case someone comes into the cabin in the winter (and we don't really want to fire up the plumbing that was carefully drained before winter), and that the water has never been frozen when they came in, even in the dead of winter. 

Estragon

My water is always frozen when I snowshoe in in the winter. Still, it's easier to thaw it by the woodstove than to haul it in or make a hole in the ice ;-)

Horsefly

Well, Vmax responded to my question. This seems like it really doesn't answer the question, but I guess I'll just be happy with the fact that they say I should be fine.

Vmax said:

Thank you for contacting us, we are glad to help you. If AGM batteries will be stored in a cold environment then we recommend to keep them connected to a charger/solar as you are doing with your system. Your VMAX batteries will be fine in the application you have described, the solar charging will generate enough heat within the batteries to keep them healthy. VMAX batteries can withstand temperatures above or below our recommended storage temperatures, please note as with any battery very cold or very hot temperatures will affect the performance of the batteries.

Please let us know if there is anything else we can help you with.

Seems like they have lawyers answering technical questions over there.

Estragon

Kind of a non-answer answer. You may be right about lawyers running the support dept.

westbranch

this has been my observation over the past 6 years with my AGMs too.
the solar charging will generate enough heat within the batteries to keep them healthy

With the CC charging daily, mine did not go below  freezing in the insulated basement
nor in the previously unheated but insulated, above ground storage room either. I did not use the MidNite Classic's  'skip days' feature.

softdown

I keep a group of old "solar" batteries outdoors and the temperature has dropped down to -30F with some regularity. The old cells with very low SG will develop a very thin skim of ice at the top. Note that these are my experimental/extra strings. 

Indoor temperatures of properly insulated structures tend to be well above outdoor temperatures....during the winter. Freezing should be the exception. Even an unoccupied car will generally offer warmer temps than found outside of the car....maybe ~10F or so.

I sure would not heat the batteries. Being cool and cold will make them last much longer. We also have several irregular posters from Canada's frozen north. My main recollection is that their batteries last much longer as a rule.

For every 10C of long term temp. decrease, batteries will last ~ 50% longer as I recall. I moved mine from the sunroom to an unheated room. This winter may prove interesting.

mcgivor

Cold temperatures basically put the batteries to sleep, retarding self discharge, as long as they are fully charged the danger of freezing is minimal, the apparent capacity will be reduced, if called on to work, but there would be no adverse affect, performance will return once the temperature rises to normal, It's unlikely one manufacturers batteries would be different to another based on chemistry, there are catch words such as nano gell and the like, but essentially they are all the same and temperature tolerance would be similar, if not identical. The attached pdf is documentation of testing of AGM and Gel batteries under extreme cold, just for interests sake.

Horsefly

Thank you all. I'm going to assume it will be fine. I'll report back here next spring if I find out different.

Raj174

At least you have their blessing if you do have a warranty issue.

Marc Kurth

Charging rate at low temperatures is not an fixed number.  I layout a lot of applications in high altitude and arctic regions, including buoys in the arctic ocean. My experience after almost 10 years of doing this is that not all AGM's are equal - or even close.

Example: If I hit AGM's like Vmax, Fullriver, Deka/MK, Trojan, US Battery, etc. with the kind of charging currents that are normal for Concorde - they would very quickly be destroyed. 

By the way, that test linked above was performed using a low end AGM (Deka) and did not have temperature compensated charging - yet they were measuring capacity........... and it still worked.

Respectfully,
Marc Kurth
Bastrop, TX

softdown

mcgivor said:

Cold temperatures basically put the batteries to sleep, retarding self discharge, as long as they are fully charged the danger of freezing is minimal, the apparent capacity will be reduced, if called on to work, but there would be no adverse affect, performance will return once the temperature rises to normal, It's unlikely one manufacturers batteries would be different to another based on chemistry, there are catch words such as nano gell and the like, but essentially they are all the same and temperature tolerance would be similar, if not identical. The attached pdf is documentation of testing of AGM and Gel batteries under extreme cold, just for interests sake.

That pdf curiously drops from 25C to -20C with nothing in between. Pretty extreme.

Horsefly

With all of @Marc Kurth's experience, I'm more convinced I'm OK.  Thanks again everyone.

Oh, and I also think I know where I'm getting my next set of AGMs (but hopefully not for a while!).

softdown

Relevant though for car batteries. Who does longevity go down in the extreme cold? Perhaps the batteries are getting hit with excessive voltage when it is cold? Perhaps a battery has to be very strong when it is -20F. Mark K would know...

Estragon

Takes more CCA to start in extreme cold, which the cold battery has less capacity to supply. More thermal stress if the battery lives near the engine. Running more accessories (heater, lights). Battery charges slower in the cold. Lots of possibilities.

softdown

Estragon said:

Takes more CCA to start in extreme cold, which the cold battery has less capacity to supply. More thermal stress if the battery lives near the engine. Running more accessories (heater, lights). Battery charges slower in the cold. Lots of possibilities.

I think the alternator supplies the power when the engine is running. I seen a car run with a very old battery that measured about 10 volts. I think they push started it every morning. No way that battery powered hardly anything. 

Seems that problems in the frozen north could largely be overcome by deploying an extra large battery. My 488 truck engine starts fine with a large 2009 battery. Benefits to a cold climate...and low usage of course.

softdown

Also....this is a VW chart and VW's often come with diesel engines last I checked. Diesel's distinctly do not like cold weather...at all. 

Estragon

I haven't measured my cars, but on my boat the alternator doesn't put out much current until the engine gets to well above idle. If the same is true for cars, it wouldn't matter for hwy driving, but short city trips with lots of idling at lights etc might mean some running on battery and/or not fully recharging?

Diesels don't like cold is right. The fuel can turn to jelly in the cold. Anti-gel additives help.

softdown

Estragon said:

I haven't measured my cars, but on my boat the alternator doesn't put out much current until the engine gets to well above idle. If the same is true for cars, it wouldn't matter for hwy driving, but short city trips with lots of idling at lights etc might mean some running on battery and/or not fully recharging?

Diesels don't like cold is right. The fuel can turn to jelly in the cold. Anti-gel additives help.

I'm not sure exactly what goes down with alternators. However I do *believe* that the alternator produces a lot more power when the battery is low. 

jonr

I've never seen temperature compensation on an automobile regulator.  So perhaps the batteries don't get fully charged when it's too cold.

mike95490

jonr said:

I've never seen temperature compensation on an automobile regulator.  So perhaps the batteries don't get fully charged when it's too cold.

Doesn't mean it doesn't exist.   98 Dodge trucks have a spring loaded BTS under the battery case, and a thermal shield around the battery, and the alternator is controlled by the ECU and the BTS.   I think since OBDII, all cars have thermal compensation on the battery voltage

jonr

Some say that automotive batteries that aren't regularly used for long trips benefit from a monthly charge with an plug-in battery charger.  No hard data, but I tend to agree.

BB.

I put a good quality float chargers on modern cars that have computers, On-Star, and such... They tend to discharge the batteries too much after 2-4 weeks of non-driving.

-Bill

softdown

BB. said:

I put a good quality float chargers on modern cars that have computers, On-Star, and such... They tend to discharge the batteries too much after 2-4 weeks of non-driving.

-Bill

That sounds like the surveillance device, I mean computer system is always on. 

EDIT: Let me guess, there are problems if the battery is simply disconnected when not in use?