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The traction battery (high voltage battery) of a hybrid car is one of the most reliable parts with a reported average life span of ten years.

Some people have used theirs way beyond that. As the car ages, the battery becoming weak is inevitable.


What is a hybrid battery?

When people say hybrid battery, they refer to the high voltage/traction battery.

It is different from the normal 12 volts type found in a conventional car.

In a hybrid vehicle, the 12 volts battery is merely used to power accessories and control units.

The high voltage battery is used to power the electric motors which drives the wheels.


What causes the hybrid battery to become weak?

1. Normal ageing of the battery can make it to become weak meaning that it served during its useful life.

2. Putting transmission in neutral at stops. This might not apply to every hybrid car that has been produced. Whenever the transmission is in neutral, the battery does not charge. This is the way it is designed to operate. This is one area where driving a hybrid is different from driving a conventional internal combustion unit cars.

3. Battery pack cooling problems can affect the cells. There is a fan unit attached to the battery pack that cools it. When this fan goes bad, the chances of the battery being affected is high.

4. Charging system problems can cause the battery to either undercharge or overcharge. Parts of the charging system that can go bad are inverter/converter and battery control unit or even the generator that also acts as moror.5. Battery sitting for long without use. This can happen if the car is parked for many months without removal of the battery fuse. The battery is going to discharge gradually until it finally becomes weak.


How do we know that the hybrid battery is weak?

1. Poor gas mileage.

Weak batteries draw high currents from their charging sources. Since the engine is responsible for changing the battery, there is a high load that is placed on the engine during charging. This in turn causes high fuel consumption as the engine needs fuel to carry the extra load placed on it.

2. Erratic battery charge state.This can be seen in the battery indicator on the dash. Now it is full and suddenly it goes to a drained state again. This is a sure call for battery replacement.

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.