If you experience the following symptoms when driving your hybrid vehicle, depending on its severity, there is a high probability that you have a weak hybrid battery pack or it is on the way to complete failure.
These symptoms are often hard to notice because most people only have one hybrid vehicle, thus there is no benchmark to measure if you have a weak hybrid battery. However, try to remember how your vehicle drove when you first bought it, or go test-drive a newer vehicle to compare.
4 Symptoms of a Weak Hybrid Battery:
Poor fuel economy
Engine gets activated frequently
Dashboard hybrid battery gauge behaving erratically
Symptoms of a Failed Hybrid Battery:
In addition to the symptoms of a weak hybrid battery pack, one that has failed will exhibit the following:
The check engine light with a message saying "Check Hybrid System" will appear along with the master warning light (triangular indicator or a symbol of a car with the exclamation mark). On some occasions, the ABS, VSC and E-brake (Yellow handbrake indicator) will appear.
The engine may start to operate full-time instead of switching to the battery.
A scan tool would provide code descriptions such as "Replace hybrid battery pack", "Hybrid battery pack deterioration", "Battery block X becomes weak", etc.
In a more severe situation, the electric A/C compressor might quit along with the engine.
Honda Hybrids (IMA based system)
The IMA light will appear.
A scan tool would provide code descriptions such as "Hybrid battery pack deterioration", "Battery module individual voltage problem", etc.
In a more severe situation, the check engine light can appear along with the red battery warning light. The red battery warning light would indicate that the 12v battery is not getting properly charged via the hybrid battery. Continuing to drive the vehicle in this state would cause the engine to stall.