# Should I use an External Battery on my Zymkey / HSM?

**URL:** https://community.zymbit.com/t/should-i-use-an-external-battery-on-my-zymkey-hsm/1041
**Category:** GENERAL
**Created:** [December 10, 2020, 7:42pm UTC](https://community.zymbit.com/t/should-i-use-an-external-battery-on-my-zymkey-hsm/1041 "2020-12-10T19:42:55Z")
**Posts on this page:** 5
**Page:** 1

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### Author: ![Michelle\_of\_Zymbit](https://avatars.discourse-cdn.com/v4/letter/m/5e9695/32.png) [@Michelle\_of\_Zymbit](https://community.zymbit.com/u/Michelle_of_Zymbit)
#### Post date: [December 10, 2020, 7:42pm UTC](https://community.zymbit.com/t/should-i-use-an-external-battery-on-my-zymkey-hsm/1041/1 "2020-12-10T19:42:55Z")

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The following table compares Zymkey and HSM operational modes while connected to Main Power, Battery Power, and No Power.

The battery is required to maintain the Real Time Clock and the perimeter detect circuits when the host power is removed. Without the battery, these two functions will not be active when the host power is removed.

![Battery Functions Matrix](https://canada1.discourse-cdn.com/flex027/uploads/zymbit/original/1X/373ded4ee1cc93a5538021eaf1a2db2d12428227.png)

For more information, reply to this post or contact a Zymbit employee directly.

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### Author: ![Michelle\_of\_Zymbit](https://avatars.discourse-cdn.com/v4/letter/m/5e9695/32.png) [@Michelle\_of\_Zymbit](https://community.zymbit.com/u/Michelle_of_Zymbit)
#### Post date: [December 10, 2020, 7:43pm UTC](https://community.zymbit.com/t/should-i-use-an-external-battery-on-my-zymkey-hsm/1041/2 "2020-12-10T19:43:00Z")

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### Author: ![Michelle\_of\_Zymbit](https://avatars.discourse-cdn.com/v4/letter/m/5e9695/32.png) [@Michelle\_of\_Zymbit](https://community.zymbit.com/u/Michelle_of_Zymbit)
#### Post date: [December 10, 2020, 11:12pm UTC](https://community.zymbit.com/t/should-i-use-an-external-battery-on-my-zymkey-hsm/1041/3 "2020-12-10T23:12:44Z")

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### Author: ![haydon](https://avatars.discourse-cdn.com/v4/letter/h/f05b48/32.png) [@haydon](https://community.zymbit.com/u/haydon)
#### Post date: [July 7, 2021, 11:30am UTC](https://community.zymbit.com/t/should-i-use-an-external-battery-on-my-zymkey-hsm/1041/4 "2021-07-07T11:30:13Z")

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If you create a product which uses the tamper detect feature on the Zymkey 4, is this not rendered useless if the battery power is depleted? I can see that the HSM 6 API allows for a self-destruct when the power drops below a threshold, can you do this for the Zymkey 4?  
Also, how long can you expect an average battery cell to last?

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### Author: ![Bob\_of\_Zymbit](https://avatars.discourse-cdn.com/v4/letter/b/82dd89/32.png) [@Bob\_of\_Zymbit](https://community.zymbit.com/u/Bob_of_Zymbit)
#### Post date: [July 8, 2021, 3:26pm UTC](https://community.zymbit.com/t/should-i-use-an-external-battery-on-my-zymkey-hsm/1041/5 "2021-07-08T15:26:20Z")

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The Zymkey 4 tamper detect circuits are inactive when there is no battery power. Typical battery life is 2-3 years off power, 3-5 years with power. The HSM6 does have a more robust battery API as you have noted. The Zymkey 4 does not have the feature to monitor the battery voltage.