To disconnect or not to disconnect battery terminals when recharging

Winter has arrived and frosts have hit many Russian regions. Some car owners have started having problems with their batteries. Low temperatures often prevent the engine from starting right away. Therefore, those who have the opportunity charge the battery. Most often, it is left overnight in the garage, connected to a charger.


But here an interesting point arises: remove the terminals from the battery or leave it connected to the on-board network car? Previously, we didn't think long - we charged without touching anything. Back then, the only electronics in the car were a watch and a radio.


Nowadays the situation is different: modern cars are literally stuffed with all sorts of devices, sensors, displays, not to mention the obligatory ECU. Therefore, any "wrong move" associated with the supply of "foreign" voltage to the on-board network is fraught with the breakdown of expensive electronics. On the other hand, modern chargers (ZU) are also "not made by a finger": they have various types of protection, current limitations, etc. So, should you remove the terminals or not?

Nuances

There is no single answer. It is necessary to consider the specific model of the car and the type of charger, as well as the battery. But there is a key point: the safety of the car's on-board electronics. Connecting a power source from the outside is an emergency, "stressful" situation for it. But this does not mean that you cannot charge the battery with the terminals connected.


The standard voltage in a car is on average 13,5-14,5 volts. Everything depends on the number of connected consumers, the generator power. Conventionally, we can say that the on-board electronics will withstand up to 16 volts. If your "charger" does not give out more, you can safely connect it to the battery without removing the terminals.

However, there may be risks here. If your charger is old, or even from Soviet times, it is unlikely to have any protection. This means that when a voltage surge occurs in the household network, it will also increase at the battery terminals, and therefore in the on-board network.


Modern "chargers" can smooth out the current to a safe level. But again: there are limits. One charger will automatically switch off at a dangerous, i.e. excessive increase in voltage, another will burn out. In the best case, itself, or the car electronics will suffer. If your household network is unreliable (for example, at the dacha), it is better not to risk it and disconnect the battery. But there is an option: use a stabilizer. It will also "protect" the charger and the car's on-board network. Or buy an expensive charger with all sorts of safety options.

About batteries

They also come in different varieties. Some of them, the expensive ones, require a strictly defined charging mode: this is specified in the instructions. And the first charger you come across will not work with them. But even with traditional batteries, things are not so simple: for example, heavily discharged calcium batteries require an increased voltage of 16,5-17 volts when replenishing their capacity. And there are chargers that will automatically supply it, “seeing” that the battery needs more current.

Why don't they want to disconnect the terminals?

It's not just about laziness: they say, they don't want to reach for the keys! Although, it's worth mentioning: in some VIP cars, you can't just get to the battery, designed for 7 years of operation: it will require difficult dismantling. And car owners are also afraid of knocking down the settings of the ECU and other electronics in the car.


But there is nothing to worry about: after reconnecting the battery, after about 100 km of running, everything will return to normal: the systems will adjust themselves. If this does not work for you and you do not want to remove the terminals, but you need to charge - read about the 100% method below.

Saving all data in the car's "brains"

For this you will need another working battery (even from a motorcycle, as long as it produces 12 V). Connect it in parallel to the one installed on the car, unscrew the terminals from the factory battery and remove it for charging. Then perform the operation in reverse order.