A traction battery is normally charged within a few hours of discharging. The lead sulphate that has formed is transformed during charging into lead, lead oxide and sulphuric acid. Newly-formed lead sulphate is easy to transform into active material again and a good charger with the right charging factor can recharge the battery to 100% of its capacity.

If the battery is subjected to incomplete discharges, the lead sulphate crystals that remain will successively form bigger and less soluble crystals that will not dissolve during a normal charge. Repeated incomplete charges further increase crystal formation and after a while diminished battery capacity begins to be noticeable. If one begins to charge intermittently instead of equalise charging, the truck runs better temporarily, but sulphation has not been halted, it only continues more slowly. 

Demands on faster charging, lower energy consumption, less water consumption and gas development also increases the risk of sulphation. Proper trickle charging such as the pulsed type our chargers use can counteract sulphation in part, but if it is advanced, an equalise charge or reconditioning of the battery is needed. 

Restoring a sulphated battery can be accomplished in many ways, depending on how long sulphation has been taking place. If the battery is only somewhat sulphated, an extra charge now and again may suffice. 

The so-called Monday charge, which is standard in all of our BTM, TTMV and MTM chargers, provides just such a supplement that freshens the battery if it has been subjected during the week to any incomplete charges. 

The BTM charger can provide a somewhat stronger equalising charge. If this function is chosen on, for example, Friday evening, first the battery is charged normally and then left to rest for 10 hours. Then it is charged again to 20% of the battery’s capacity. 

The best way to charge a severely sulphated battery is with low average current over an extended period of time. 

The most common and easiest method is to charge using a current of about 1% of the battery’s rated capacity for 2 to 14 days, depending on the degree of sulphation. If the charging output is limited so that too high a temperature is avoided, lead sulphate crystals can also be dissolved using some kind of pulse charge, similar to the trickle charge we use in our unregulated chargers. 

It is however important that the charging output is limited, since practically all energy fed to the battery during reconditioning charging turns into heat and gas generation. 

We have a special charger for reconditioning severely sulphated batteries. The newest one is called the SMP 120/10 – a small, handy power supply (1.6 kg) that can charge with 10A up to 80V and then with output limitation of 800W up to 120V. The SMP can be used to recondition anywhere between 1 and 40 cells. 

The TTMV and MTM charger can easily be reprogrammed by setting the UH charge’s voltage level to 2.80 V/cell instead of 2.26 V/cell. Since it is normally programmed with a maximum UH charging voltage of 4% of I5, current during reconditioning will be 0,8% of the Ah value. If this current is reprogrammed to 2% of I5, reconditioning takes longer but it will be more efficient. Choose this programming during up to 4 weeks if you suspect that the battery is severely sulphated. Measure the battery’s acid weight periodically after complete charge. As long as this increases in any cell, you can continue. When the cells are equalised or acid weight no longer rises, you changed the UH voltage to 2.26 V/cell and maximum UH current to 4% again. 

It is important to point out that most batteries are not sulphated when capacity diminishes – they have just reached the end of their service life. In these cases, reconditioning can only extend life for a shorter period. It is only when the battery has been subjected to repeated incomplete charges over an extended period of time or if it has been uncharged for a time that reconditioning has much effect.