Toyota Prius hybrid battery mystery leak

Battery leakage

Whether it’s your child’s toys, your flashlight, your remote control, or anything else that’s battery-powered with liquid or semi-solid electricity, there’s always the possibility that the battery cell will deteriorate and become damaged at the very least. In the worst case, it poses a health risk.

Do Prius batteries ever leak?

That’s been the takeaway message of late Toyota maintenance YouTube channel episode in which the host “show and tell” a 2015 Prius with 103,000 miles on which a customer complained about a potentially suspicious-looking hybrid battery leak that he discovered while taking the spare tire out of the trunk.

The strangeness of what seems like an obvious case of the “if it looks like a duck, walks like a duck, quacks like a duck—then it must be a duck” scenario is why there is no check engine light, check battery light warnings on the dashboard, or even Scan tool code that lets you know there’s something less than optimal about your car’s hybrid battery? It’s a mystery.

Related article: The truth about owning a Prius and its battery

An internet search reveals very little that Prius models have ever had any battery leakage issues with the exception of some earlier batteries where the terminals were noted to leak at their connections and cause corrosion.

Hints about the mystery

During the host’s presentation, we are left with the following hints about what might happen:

• The car went ashore as evidenced by sand on the trunk floor, so exposure to salt water may have been the cause.
• There is no evidence of soft drink spills or other household-related mess incidents.
• Corrosion appears to only occur at the bottom of the hybrid battery and not at the high voltage terminal connections.
• The corrosion you see is a combination of reddish metal oxidation corrosion and the typical off-white crystalline mess of the battery terminal that you find with leaky batteries.
• The hybrid battery has reached or is very close to its expected life.

Actions taken by the host

Rightly so, the host stopped his investigation after removing the hybrid battery panels and advised the car owner to take his Prius in for an inspection by a Toyota dealer’s garage. Primarily because this may be a defective hybrid battery and there may be some compensation despite the fact that the car’s warranty coverage has just passed the 100,000 mile mark, duh!

There is another good reason for this inaction: the battery poses a potential health risk that could affect the health of the owner and his family. By not disassembling the battery any further, this prevents the battery issue from being ambiguous in the event that there is a lawsuit and Toyota claims that someone else handling the battery is the cause of any damage that may be found.

Watch the video and guess

Follow along with the host in the video and see if you can come up with other sources or reasons that could explain the hybrid battery mystery.

My best guess

From a previous article about Prius hybrid batteries, we learned that corrosion can occur under the battery bus bar cover of the Prius battery over the years, presumably caused by wet conditions over time.

Since there is what looks like beach sand in the trunk, it is possible that the Prius was parked on the beach close enough to the water to be exposed to actual water entering the trunk or enough salt spray in the air to cause a corrosion problem.

However, I would like to put forward an alternative theory: rodents. Rodents love parked cars because they are a good source of crumbs. And if you’ve ever seen traces of rodent urine on metal, what you see in the video looks suspiciously similar.

While it appears the mystery has not been solved yet, be sure to watch a follow-up video of this Prius issue. If there is an answer, the host will likely share it in a future video for their followers.

For additional articles related to Prius hybrid batteries, here are some to consider:

Timothy Boyer is an automotive reporter based in Cincinnati. He has experience in early car restorations, and he regularly restores older vehicles with engine modifications to improve performance. Follow Tim on the Zen and the Art of DIY Car Repair website, the Zen Mechanic blog and on Twitter at @TimBoyerWrites And Facebook for daily news and topics related to new and used cars and trucks.

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