2004–2009 Toyota Prius: Hybrid battery failure (red triangle, poor mileage)
Likely causes, ranked
- Aging hybrid battery modules$999–$3,200Shop
- Battery cooling fan cloggedDIY
- 12V battery or sensor problems mistaken for HV failureDIY
Real-owner fix counts will appear here as reports come in.
Rough cost: $999–$3,200DIY or shop: See DIY or shop section
Parts to check
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Symptom: A red triangle warning, the battery gauge swinging quickly, weak acceleration, and lower mileage.
Likely causes
- Aging modules. PriusChat's owner survey shows most gen-2 batteries lasted past 150,000 miles, but some failed earlier.
- Cooling fan. A clogged fan can overheat the pack.
- Look-alikes. A weak 12V battery or a sensor fault can cause similar warnings.
Rough cost range
| Repair | Reported |
|---|---|
| Replacement | About $999–$2,099 aftermarket installed; about $2,500–$3,200 new OEM (Greentec, owner reports) |
DIY or shop?
Shop. Cleaning the fan is DIY.
Useful steps
- Read the hybrid codes.
- Clean the battery fan intake.
- Compare refurbished and new pack options.
Vehicle focus: 2004–2009 Toyota Prius.
Safety / mechanic note
High-voltage work is dangerous. Leave the pack to trained techs. Verify with a mechanic.
Related trouble codes
Recalls & service bulletins
No recalls or service bulletins are listed for this page yet.
NHTSA complaints: 292 keyword-matched complaints (of 7,093 unique complaints filed under NHTSA model names PRIUS, 2004–2009; NHTSA complaints API by model year, queried 2026-10-15).
Always check your VIN for open recalls at nhtsa.gov/recalls.
Sources
What actually fixed it?
Had this problem? Tell other owners what the real fix was. Reports are counted above; we never show made-up numbers.