Long Term Storage Of High Voltage Battery

You could get a charger/rebalancer (I have a Supermate DC6) and do a recharge of each of the 28 modules every few months to keep it charged to 80% SOC. Seilerts says not to store the battery at 100% as that can cause it to overheat. Remember to rebalance all the modules before installing the replacement battery.

JeffD

 

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Edit, link with some technical information about storing NiMH batteries.
Understanding your HEV NiMH battery pack - CleanMPG Forums

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• Self discharge rate is very high often dwarfing all other competing chemistries. That is why hybrid cars should be powered up at least once every 30-60 days to prevent a full and crippling charge depletion. The SoC indicators ARE NOT a reliable indicator of health when a vehicle is in storage.
• • Requires cell reconditioning if SoC is kept at a steady level for longer periods of time
  What can be done to ensure a longer battery pack life?
  • Cause a deeper discharge periodically to nullify the inherent memory effect. This is automatically done by the governance and battery management systems.
  • Ensure that the amplitude of your regenerations and electric assists are as small as possible.
  • Use some electric assist once in a while. Please remember a static SoC is just as bad as excessive use.
  • Keep your battery pack cool. While there are many things we can do some do not involve hardware modifications at all
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Add 1 amp hour with a charger every 6 months. I would not charge a battery to full under any circumstance if it were not going straight into a car. Or swap out the batteries every 6 months. You may want to swap it right now, since you have no idea if it is any good or not.