3. Battery cooling fan speed/noise increases.
Weak batteries tend to draw more current and thereby generating more heat. This is why the fan kicks into action often to protect the battery unit from destruction due to heat. The fan noise is as a result of the fan working at full speed. We have a detailed article on this.
4. Engine kicks in more frequently.
A weak battery does not retain charge for long. Within a short time, it gets depleted and the control unit sends a signal for engine start in order to charge the battery.
5. The engine running for a long time before going into battery mode.
As said earlier, it takes time for a weak battery to reach full charge. Unfortunately, the battery cannot retain the charge as the battery runs down quickly.
6. Reduced charging and discharge time.
You may notice that battery quickly gets full and also quickly gets drained. At this stage, the battery has almost totally gone bad.
7. The car goes off at random on motion. Many users have reported this symptom when the hybrid battery is weak. There are a number of reasons why a hybrid car may shut off when being driven.
8. Starting difficulty. The 12 volts battery is merely used to power accessories. It is the high voltage battery that drives the motor in the transmission to start the internal combustion engine. When it is weak, the car might not start.