Incident during ACC II battery charging at Petzl V. Access

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In March 2013 charging of an ACC II battery failed at Petzl V.Access. The failure caused heat development and an explosion like cell ventilation as a consequence.

ActSafe has been investigating this together with our battery manufacturer. The cause is believed to be an aged/used battery with a damaged cell in a condition that did not allow detection by the Battery Management System. Charging of the battery was allowed when it should not have been. Charging the damaged cell made the standard charging algorithm no longer reliable and too much energy was allowed to enter the cell generating heat that developed into a thermal runaway.

This incident emphasises the importance of making the users aware of the risks associated with aged/used Lithium-ion batteries and to understand that:

  • Power ascenders are an extremely demanding battery application and this contributes to a relatively short service life for the batteries (compared to other much less demanding battery applications such as a power tools, computers, electric bikes etc.).
  • Lithium-ion batteries in general degenerate over time, they age. They may only last two to three years, even if they are properly stored on a shelf and unused.
  • The Lithium-ion cells used in ActSafe batteries represent a new battery technology. As the general experience grows around this battery technology in various applications the cell manufacturers are adjusting their recommendations for use. ActSafe adjusts the Battery Management System accordingly.
  • ActSafe continuously improves the battery and the Battery Management System as we gather experience on battery use in power ascenders.

The conclusion is that older batteries and batteries showing poor performance must be taken out of service and be replaced by new ones. Therefore ActSafe in co-operation with our battery manufacturer have decided to set a maximum service lifetime for power ascender batteries.

Batteries must be replaced:

  • After 24 months or
  • When less than 80 % of the initial capacity remains

For batteries already sold the end-user should calculate 24 months from the date the battery was purchased. This means that all batteries without individual serial number marking are overdue and should be replaced. A user with a battery not frequently used that are older than 2 years and still with a capacity > 80% of the initial capacity may at his own risk continue to use the batteries for an extended period of another 6-12 months. He should however be aware of the increased risks and the battery must not be charged unattended.

From the 15th of June 2013 all batteries from ActSafe will be marked with an expiry date. The expiry date will be set so that it will allows batteries to be stored a couple of months at the distributor, ensuring the end-user will have 24 months of service life.

In addition to a maximum service life for batteries ActSafe are taking the following actions:

  • A Battery Safety and Handling information folder will be distributed with all batteries as well as ascenders that are in for Service and inspection.
  • The battery information folder can be viewed/downloaded here:
  • BMS update to allow individual cell voltages to be measured before charging, thus increasing the probability that cell failures are adequately detected. (This update was introduced by end of April 2013).
  • Further BMS development to ensure a pre-charge check in order to check cells/battery condition before normal charging procedure starts.

Finally it is important to point out that a sophisticated BMS, can considerably reduce incidents, but cannot eliminate all of them. The BMS itself could break down or a battery cell might have an internal weakness not detectable during the manufacturing process. It is not possible to design a totally failsafe BMS. (Compare recently published battery problems encountered by an airplane manufacturer despite redundant BMS, a failure could not be prevented.)

For any questions around batteries please consult ActSafe directly.

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