- Measure the voltage at the battery terminals using an accurate voltmeter. If the voltage is below 10 V, the charging current will be very low, and it will take some time before the current in the battery exceeds a few mA. Such a low current may not be detectable by ammeters commonly available under normal conditions.
- Set the charger to high current.
- Some chargers have a protection circuit that prevents charging if the charger wires are connected incorrectly. A completely discharged battery may not develop enough voltage to turn on the charging circuit even if the wires are connected correctly. As a result, it appears that charging current will not flow through the battery. In this case, you should use the charger manufacturer's instructions to bypass the protection in order to charge a battery with a low voltage level. Chargers differ in the voltage and current they produce. The time required to achieve measurable currents in the battery at different voltages can be as follows:
| Voltage, V | Time, h |
| 16.0 and above | up to 4 |
| 14,0-15,9 | up to 8 |
| 13.9 and below | up to 16 |
If the charging current still cannot be measured after the specified time, the battery must be replaced.
If the charging current can be measured during the charging time, the battery is considered good and charging can be completed normally.
It is important to remember that a completely discharged battery must be charged to a sufficient ampere-hour capacity to be usable. As a rule of thumb, the reserve capacity of a battery can be used as an indicator of the ampere-hour rating; at this point the indicator on the hydrometer will turn green.
For example, if it is determined that the battery reserve capacity of the boom lift is 75 minutes, the following mode will be required to fully charge it:
Charging with a current of 10 Ax7.5 h = 75 Ah or charging with a current of 25 Ax3 h = 75 Ah, etc.
It is recommended that each battery charged using this method be subjected to a load test.
Caution: A deeply discharged battery must never be charged using a fast charger.
Quick charge/start of the engine from the auxiliary device
- The battery should only be charged using a fast charger in exceptional cases. The same applies to the load on the battery during engine starting from an auxiliary device. During fast charging, the charging current is 20% or even more of the battery capacity. When fast charging, the battery is damaged because it is exposed to a large current for a short period of time. Batteries that are deeply discharged or have been stored for a long time cannot be charged using a quick charger, as this will cause what is known as surface charging.