Exploring Battery Charging in Unheated Garage at Sub-Zero Temperatures (-20°C, -15°C, -10°C)

I was looking for information on this topic on the forum and on the net, but nothing specific can be found.
Specifically, charging the battery in an unheated garage, for example, when the temperature is -20 ° C -15 ° C -10 ° C outside.

In general, I found statements that I would rather not load, threat of an explosion, but no specific studies.

I would prefer to avoid taking the battery out of the car. There are later problems with the electronics. You can find information on what upper temperature should not be exceeded, but nothing about the minimum temperature.

Hello,
In item 4 on the page:
http://www.mototechnika.republika.pl/pliki/akumulatory.html
it describes exactly how the temperature affects the battery parameters.
Besides, the batteries are charged at such low temperatures when the vehicle is running and nothing happens (it does not explode, etc.).

And they say that the electrolyte temperature ranges from 5 to 40 ° C.

The electrolyte density is based on 25 ° C. At -25, even when charged it will be different. Also, a charged battery at -25 ° has 60% of its power.
I am looking for a specific theory, let's say academic, describing the topic.
I know that the battery is charged while driving, but you can find various opinions on this subject, unsupported by anything.
The most effective charging is at 15-25 ° C. Does -25 make sense?

kaputo wrote:

e.g. in an unheated garage when the outside temperature is -20 ° C -15 ° C -10 ° C.
In general, I found statements that I would rather not load, threat of an explosion, but no specific studies.
I would prefer to avoid taking the battery out of the car. There are later problems with the electronics. You can find information on what upper temperature should not be exceeded, but nothing about the minimum temperature.

The principles of charging at low temperatures are the same as at high temperatures. It can explode in the same way as with high ones (hydrogen is released). At the same time, it should be borne in mind that charging is ineffective at low temperatures. Charging efficiency drops proportionally as the temperature drops. After charging, you will not get the rated capacity, only the one that the given temperature will allow you to do. At -15 deg it will be somewhere with 60% capacity when fully charged. You do not have to pull out, but unhook, at least one clamp from the car. Well, unless you have a charger that prevents voltage higher than ~ 14.5V on its terminals. Otherwise, the electronics may be damaged.

Automatic chargers have a program for charging the battery at low temperatures - the end of charge threshold voltage is different.

During charging, the temperature of the electrolyte will rise ...

tzok wrote:

Automatic chargers have a program for charging the battery at low temperatures - the end of charge threshold voltage is different.
During charging, the temperature of the electrolyte will rise ...

I can assure you that it will not increase by a degree when charging in the cold. Unless you can pass some powerful current through the battery. Usually, however, rectifiers give at most a few A, which at very low temperatures does not increase the temperature in a significant way.

^ToM^ wrote:

I can assure you that it will not increase by a degree when charging in the cold. Unless you can pass some powerful current through the battery.

I would argue here, although I did not check it organoleptically - nevertheless, the alternator voltage regulators contain a therm-sensitive element to regulate the charging voltage as a function of the external temperature, I have a fairly advanced inverter rectifier with a temperature probe to correct the current with the change of battery temperature. Also note that when the battery is fully charged, when overcharged with voltage, its temperature increases as the electrolyte gasses.

robokop wrote:

I would argue here, although I did not check it organoleptically - nevertheless, the alternator voltage regulators contain a therm-sensitive element to regulate the charging voltage as a function of the external temperature, I have a fairly advanced inverter rectifier with a temperature probe to correct the current with the change of battery temperature. Also note that when the battery is fully charged, when overcharged with voltage, its temperature increases as the electrolyte gasses.

The problem is that as the temperature drops, the internal resistance increases proportionally. The apparent decrease in capacity is precisely related to the increase in Rw. Hence, when at 20 degrees C through the battery you manage to pass, for example, 4A, then at -15 degrees C I give myself 0.5-1A. This means that the increase in heat generation is not able to exceed its emission and thus the temperature does not increase. An ordinary rectifier usually works in such a way that the current drops practically to zero as the voltage increases at the terminals. So in this situation, even when the battery is gassing, the flowing current is small and is not able to raise the temperature in a measurable way. The compensation sensor in the alternator is more needed the other way. The charging voltage is to be corrected -20mV / deg C and it is quite critical with the increase, because it has an impact on the battery life.

I have a 10A automatic (impulse) charger and it stabilizes the current, not the voltage, and in the "winter program" it charges up to 14.7V (but only 7A) and not to the standard 14.4V. At -15 * C I did not charge, but around 0 * C the battery got noticeably warm.

gentlemen. The battery is charged with a charger only at temperatures above 5 degrees C. Then we only choose the method of charging, i.e. formatting, complementing and the last one is necessarily quick. and everything is decided by the amperage.

robertos.moc wrote:

gentlemen. the battery is charged with the charger only at temperatures above 5 degrees C.

Note that the "chargers" that are built into all cars charge at all temperatures. Even when it's outside -30st. Hence, the charging temperature is not critical, while the charging efficiency at sub-zero temperatures is low.

you look like a charger too. the alternator is designed to recharge the battery and the main task is to power everything you turn on. recharging in this case is possible because your battery has been energized.

robertos.moc wrote:

you look like a charger too. the alternator is designed to recharge the battery and the main task is to power everything you turn on. recharging in this case is possible because your battery has been energized.

Hence I wrote "charger". Recharging is possible at any time, even when the battery is discharged to "zero". There is no such thing as "agitation" here.

Temperature affects the rate of chemical reactions in the battery, which affects the battery capacity. In the range from 18 degrees to 27. Increasing the temperature by 1 degree causes an increase in capacity from 0.5 to 1%. At -15 degrees you can charge, but it will take much longer.