# Zymkey 'failure' after external power loss **URL:** \ **Category:** ZYMKEY4\ **Created:** [September 27, 2019, 10:04am UTC](https://community.zymbit.com/t/zymkey-failure-after-external-power-loss/653 "2019-09-27T10:04:27Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![taospartan](https://avatars.discourse-cdn.com/v4/letter/t/ce73a5/32.png) [@taospartan](https://community.zymbit.com/u/taospartan)\ **Post date:** [September 27, 2019, 10:04am UTC](https://community.zymbit.com/t/zymkey-failure-after-external-power-loss/653/1 "2019-09-27T10:04:27Z")
While running a rpi 3b with a zymkey 4i fitted correctly and in production mode, I decide to try and power the unit from an external battery rather than bench PSU. I completely forgot about the rpi and returned to it the next day and found the external battery was now flat and obviously the rpi powered off. I attached the rpi back to the PSU but found that the error “ERROR: no zymkeys installed” which is quite odd as its still in place as i left it. Please could someone explain what has occured to cause this failure? I’ve triple checked the bench PSU and its suppling the correct voltage and current. Many thanks Tao ---
**Author:** ![Phil\_S\_Zymbit\_1](https://avatars.discourse-cdn.com/v4/letter/p/45deac/32.png) [@Phil\_S\_Zymbit\_1](https://community.zymbit.com/u/Phil_S_Zymbit_1)\ **Post date:** [September 27, 2019, 4:15pm UTC](https://community.zymbit.com/t/zymkey-failure-after-external-power-loss/653/2 "2019-09-27T16:15:42Z")
@taospartan, interesting symptoms.🤔 A few questions 1. Does the zymkey have a coincell battery in it ? 2. If yes, can you measure/communicate the voltage on that coincell battery 3. Are you using tamper detect ? 4. If yes, how have you armed the tamper event ? - self destruct, or notify ? 5. What voltage & current is your bench supply deliverying? If you prefer to go to a private communications - send to [support@zymbit.com](mailto:support@zymbit.com) Thanks