Volvo Service Bulletin 3-30-03

Product Section Group No. Date Title
B 3 30 03 11.81 Maintenance of Batteries

Description: Maintenance of batteries in storage

Lead Acid battery state of charge graph

To ensure that batteries are always properly charged and in good condition when a body-built bus is delivered, we have decided to require more stringent rules concerning the storage of batteries and their charging during the time the coach body is being built. It is particularly unfavourable to batteries if a chassis has to be stored for a long period while waiting for the coach body to be built on or in connection with lengthy shipping. The person responsible for the chassis must also be responsible for ensuring that the batteries get the attention they need. A battery which is allowed to remain flat causes plate sulphation, which can result in the battery never attaining its original capacity again even if it is charged repeatedly afterwards.

The new, tighter control, therefore, involves the following measures:

It is the responsibility of the importer to ensure that the above regulations for charging batteries are adhered to.

Charging batteries

Normal trickle charging should be applied for regular re-charging. Charging period will depend on the size of the battery, the extent to which it is discharged and the charging current. By regularly applying trickle charging instead of so-called "maintenance charging" (here the batteries are charged all the time with a low current), continuous supervision can be avoided.

If a battery charger with constant-curent control is used, a charging period of 16 hours is recommended. Constant-current control means that the set current is maintained constant irrespective of whether the battery voltage rises during the charging. In this case, the charging current required to get the battery fully charged can easily be calculated once the specific gravity has been established.


The above calculation cannot be applied when using a battery charger with dropping current control. The charging current is then dependent on the battery's counter-voltage and is higher at the beginning of the charging when the battery voltage is low. During the charging, the battery voltage rises and the charging current then gradually reduces.

In this case the charging must be discontinued when the battery's specific gravity no longer increases, in spite of further charging for approx. 2 hours. The specific gravity of a fully charged battery is 1.27-1.29.