Tech Tip: Does it hurt hybrid vehicles to sit for extended periods of time?

You may have heard that it isn’t good to allow hybrid vehicles to sit for extended periods of time without driving them.  The primary reason for this is due to the effect this has on the high-voltage battery.  Nickel Metal Hydride (NiMH) batteries suffer from high self-discharge, so when the vehicle sits for extended periods of time the state of charge can drop significantly.  The self-discharge rate is affected by things like ambient temperature, state of charge of the battery (initially), and the overall condition of the battery (aged batteries tend to have higher self-discharge rates).    

So how does this affect you when working on these vehicles?  Recently I’ve heard from two shops that had taken in an early (2001-2003 vintage) Toyota Prius for repair work.  In both cases the repairs were non-hybrid drive related, and in both cases the vehicles ended sitting for several weeks prior to the repairs being completed.  The condition of both vehicles prevented the engines from starting, which meant they were unable to charge the high-voltage battery.  

When the repairs were completed the shops found that the vehicles wouldn’t “power up.”  In other words, the high-voltage battery self-discharged so much that it was unable to start the engine.  Obviously this put the shops in a very difficult situation as their options for repair of the high-voltage battery were very limited and relatively expensive (on top of the costs already incurred to repair the non-hybrid drive system). 

So how should you handle hybrid vehicle repairs to avoid ending up in that situation?  

  • Find out how long the vehicle has been inoperative prior to coming to your shop.
  • Ensure a hybrid vehicle that can’t be started and/or driven is repaired as quickly as possible to avoid excessive self-discharge of the high-voltage battery.
  • Inform the customer about this potential issue PRIOR to beginning any work on the vehicle if that work will result in the vehicle being inoperative for any significant amount of time.  

Information provided by: AR&D

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