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How to charge a calcium battery correctly

The frequency of this operation depends on the correlation between the automobile generator power and consumer power, and on the driving conditions. In the summer, almost any car can do without battery recharge. The engine starts easily, permanent consumers are ignited, electric petrol pump (about 8–10 А), car stereo (3–4 А), headlights with tail lamps (13 А). Even when idling, a well-functioning generator provides 40–45 А, which is almost enough to power the minimum number of consumers. When driving, e.g. on the highway, 60–70 А produced by the generator are sufficient to power the consumers and to charge the battery.

Battery operating conditions in winter are much more difficult. Negative temperatures reduce battery capacity, deteriorate the ability to accept a charge, and a cold engine start requires more energy. New powerful consumers start functioning onboard: heater (5–7 А in first gear and 10–11 А in second gear), defroster lines on windows and mirrors (16–20 А), seat heater 5 А. The total current consumption exceeds 50 А. When idling, the generator can no longer handle powering of the consumers, most of the energy is provided by the battery. During driving, the possibility of the generator recharging the battery appears to be very modest as well; besides, at negative temperatures of the electrolyte, the battery does not accept a charge. Eventually, the battery becomes chronically undercharged. The user may fail to notice it, since even a partial charge is normally enough to start the engine. However, chronic undercharging results in plate sulphation, which reduces the capacitance and increases internal resistance. In turn, this leads to reduced working life of the battery and deteriorated starting characteristics. Therefore, in winter a systematic recharging of the battery is required.

How often to recharge the car battery?

Recharging frequency depends on the vehicle, weather, and driving conditions. For cars with well-adjusted starting system, in mild winter conditions with daily trips over short distances with frequent traffic jams, it is enough to recharge the battery once a month or two. Clearly, if the frost reaches −30°, and each start requires multiple engagements of the starter, it makes sense to check the battery charge level more often.

And by all means, the battery should be immediately put on recharge if you discharged it to “zero” by unsuccessfully trying to start the engine. “Immediately” here is literal, since the electrolyte density in the discharged condition is low and there is a probability of the electrolyte freezing and thus damaging the battery. On the other hand, a battery remaining in the discharged state is prone to plate sulphation.

Electrolyte density reduced to 25°С, g/cm3 Freezing temperature, °С
1.09 -7
1.12 -10
1.14 -14
1.16 -18
1.18 -22
1.20 -40
1.23 -43
1.24 -50
1.26 -58

There are several battery charge modes: direct current, direct voltage, a combination.

Basic States of a Deeply Discharged Battery


1. The battery has been in a discharged condition for a maximum of 2 weeks, at room temperature, and has not been operating in a car. Charging of such a battery is normally recommended with a current equal to 0.1 of rated capacitance (6 А for 60 Аh battery) to achieve ρ = 1.27–1.28 g/cm³. The charging process can take up to 24 hours. If it is impossible to control the electrolyte density with an areometre, then use the charge level indicator, if there is one on the battery cap. Green color of the indicator means the charge ≈ 50 % (ρ = 1.23 g/cm or higher). Another sign of completed charging of the battery is “boiling” of the electrolyte and battery body temperature reaching ≈ 40°С.

2. The battery has been discharged for a prolonged period (plate deep sulphation occurred).

What is plate sulphation?

During charging of a normally discharged battery, small lead sulphate crystals can easily transform back into lead metal (negative plate) and PbO2 (positive plate), constituting plate active material. However, if the battery is left in the discharged state, lead sulphate starts dissolving in the electrolyte until its full saturation, and then settles onto the plate surface in form of large and practically insoluble crystals. They deposit on the plate surface and in pores of the active material, forming a continuous layer, which insulates the plates from the electrolyte and impedes it from penetrating into the bulk of the active material. As a result, large volumes of active material become “excluded,” and the overall capacitance of the battery is significantly lowered.

Such batteries are restored through the so-called stepped mode:

  • start charging with current 0.1C20 ≈ 16 hours;
  • discharge, e.g. using the set of car lights for 2–3 hours;
  • charge with current 0.1C20 until full charging.

Battery Charging Recommendations

Check the battery state by measuring the open circuit voltage. The voltage on the battery terminals is measured in 6–8 hours after the engine stops. If the battery open circuit voltage is below 12.5 V, the storage battery has to be recharged. Perform this check once every 3–4 months.

Charging effectiveness primarily depends on the type and quality of the battery charger. Over half of the battery chargers available on the market are incapable of fully charging the battery. Battery chargers intended for automatic operation are often pre-set for voltage 14.4–14.5 V. After reaching this voltage, the green indicator turns on, signaling the end of charging, and the charge current is automatically reduced almost to 0. Before making a purchase, study the battery charger specifications. The battery charger should provide output charge voltage of 16.2 V. Before starting to charge the battery, carefully study the battery charger instructions – they should contain a detailed description of all technical characteristics, operating rules and procedures. The battery is considered to be charged once the electrolyte density in all cells reaches the level of 1.27–1.28 g/cm³, “boiling” of the electrolyte at the end of charging, and once the battery body reaches the temperature of ≈40°С.