Battery technology has changed considerably over the past few years, with new technologies and concepts improving performance and service life.   Keeping batteries properly maintained is essential and the following technical data gives an insight into what is involved.

The Task of the Battery Charger

The task of the charger is to recombine the active material; sulphuric acid (H2SO₄), lead (Pb) and lead oxide (PbO₂) from the lead sulphate (PbSO₄) that has been generated during discharge. Indeed, lead sulphate is the same material that causes the fault known as sulphating.  Lead sulphate is necessary throughout the entire process, but it is when the crystals of lead sulphate grow larger that the trouble begins.

A charge graph, or to be more precise a charge algorithm, shows how the battery acquires energy over the full charging process. A DIN-standard, 41773, provides guidelines on how an algorithm of this type is structured, but the most important thing is the know-how associated with the treatment of a battery in order for it to remain in the best possible shape so as to achieve the goal of the longest service life and highest capacity. Bear in mind that there is no universal method to solve all the problems in an optimum way. The battery can be manufactured in a number of ways, and you need to consider both the battery itself together with the way it is used, which gives rise to a great number of algorithms. These differ sharply between a modern multi-step switch mode charger and a linear transformer charger of the type you will find at a car spare parts dealer or a discount store.

A couple of interesting details from the graph:

• The linear charger is indeed marked with a high Ampere number, but this is often measured using a battery that is as low as 5-6V. A more realistic number is 75% of the rated current power, but this drops quickly when the battery voltage starts to rise.
• The switch mode charger falls a little behind at the start as regards the amount of energy given to the battery but soon catches up.
• The linear charger has difficulty filling the battery despite being at a high voltage with the charger emitting little current but a lot of heat without providing that much charge to the battery.
• A charger that cannot provide a constant voltage cannot fully charge a battery without reaching a range where the battery starts to gas and loses fluid. A rule of thumb is that you will get 80% of the charge during the initial phase. Some chargers with a more basic control go down to a lower voltage when 14.4V has been reached, but then it can take weeks to get the remaining 20% of the charge.

Sulphated Batteries and CTEK Desulphation

A "lightly sulphated" battery has a layer of insulating lead sulphate on its plates. When you try to charge a battery in this state, the voltage rises quickly, as per Ohm's law, and for an uncontrolled charger it rises all the way up to its maximum. It is often said that these batteries "will not accept a charge". However, they can sometimes be "revived" by charging them with a low current over several days. Another way is to raise the voltage to 20-25V in order to get the battery to charge a little. This may work with a battery that has been protected on a workbench, but it is risky for the vehicle when the battery is still connected to the mains. Many manufacturers including BMW motorcycles, have prohibited the use of this type of charger without first disconnecting the battery in the vehicle. This may result in you losing the settings for your radio and sometimes even for the engine control unit, which makes this method of desulphation a lot more labour intensive.

Another more efficient method is applied by CTEK chargers. They charge at full current right up to maximum voltage whereupon the charger returns to zero. Charging starts up again immediately and keeps on in this way by sending pulses of energy to the battery. You can see this as the lamps in the upper row are flashing. If they are still flashing after 60 minutes, you will have to accept that the battery is spent, but if a lamp indicating CHARGING is lit permanently, you have succeeded in reviving the battery. Bear in mind, however, that the battery is probably at the end of its service life and will need to be replaced sooner rather than later.

 1. Desulphation
Runs a complete charge cycle within a fraction of a second. The cycle repeats during the whole desulphation phase. Every cycle recovers some lead sulphate into useful material.

2. Start
Starting phase for charging. Charging with limited charging current. The starting phase is over when the voltage rises above 10.5V, at which time the charger switches to bulk charging.

3. Bulk
Charging where 80% of the energy is returned. The charger delivers maximum current until the battery voltage has reached the set level.

4. Absorption
Final part of the charge up to 100%. The battery voltage is kept constant at the set level, during which time the current drops gradually.

5. Pulse
Maintenance charging. The state of charge varies between 95% and 100%. A pulse is sent out to the battery if the voltage drops. This keeps the battery in trim when not in use. The charger can be connected for months at a time.

6. Setting: Supply
The supply mode setting supplies a constant voltage at 13.6V and current up to 7A. It could be used for maintenance charge using the float approach. This approach keeps the battery at 100% state of charge, but the constant small overcharge also increases water loss.

7. Setting: Boost 16V/1.5A/4h
The Boost setting gives a constant current at 1.5A, maximised at 16V for four hours. It will automatically switch to 14.4V pulse setting after four hours.

This mode is used for batteries that have been severely discharged.

Information and illustrations taken from the Ctek Website