Annual hybrid battery service — catch a weak block while it's still one block

Nickel-metal hydride packs age faster at high temperature, and Phoenix supplies about five months a year of it. On top of that, Toyota and Lexus cool these packs with cabin air — so dust, pet hair and cargo pushed against the intake vent directly raise how hot your pack runs, every day, for years.

Both of those are gradual. Neither sets a warning light until the damage is done. An annual check is the only realistic way to see it happening while you can still do something about it.

1. 1Block-level voltage and internal resistance across the whole pack, so we can see the spread — not just whether it passes.
2. 2Comparison against last year's numbers if we've seen the car before. The trend matters more than any single reading.
3. 3Rebalancing, so the blocks start the year at a matched state of charge instead of drifting further apart.
4. 4Replacement of any block that has clearly fallen behind the rest, while it's still one block.
5. 5Cooling intake, filter and duct inspected and cleaned — this is the step most owners have never had done.
6. 6Cooling fan operation and actual airflow verified, not just visually checked.
7. 712V battery load test, because it fails on its own schedule and strands people.
8. 8A written record of the numbers, so next year's comparison means something.

• Anyone who has just had a pack replaced or reconditioned — protecting that investment is the entire point.
• Cars that carry pets, or live on dirt roads around Cave Creek, Carefree, Rio Verde or New River. Cabin air is battery cooling air.
• Family SUVs and minivans where cargo and car seats sit against the rear-seat intake vent.
• High-mileage commuters and rideshare cars putting serious cycles through the pack.
• Cars that sit for months — seasonal residents in Scottsdale, Sun City and Fountain Hills. Sitting hot is its own kind of stress.
• Anyone planning to keep the car several more years.

If the numbers say a Prius pack is past saving, the replacement options for each generation are on our Prius battery replacement in Phoenix page.