# Photon and back-up battery

**URL:** <https://community.particle.io/t/photon-and-back-up-battery/12286>\
**Category:** Hardware\
**Created:** [June 3, 2015, 8:16am UTC](https://community.particle.io/t/photon-and-back-up-battery/12286 "2015-06-03T08:16:35Z")\
**Posts on this page:** 1\
**Showing post:** 16

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**Author:** ![AndyW](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/andyw/32/686_2.png) [@AndyW](https://community.particle.io/u/AndyW)\
**Post date:** [June 10, 2015, 3:59pm UTC](https://community.particle.io/t/photon-and-back-up-battery/12286/16 "2015-06-10T15:59:08Z")

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You might find this thread useful also.  
It discusses using a supercap rather than a battery, but the use case is similar to yours.

> [@Photon VBAT supercap circuit](https://community.particle.io/t/photon-vbat-supercap-circuit/12390):
>
> When I get my Photon, I’d like to use a supercap to keep the RTC synchronised in the face of power outages. After some reading and some number crunching, I came up with this: Edit: added D2 as per discussion. My calculations below still reflect the circuit without it. [image] (Updated schematic from post [#41](https://community.particle.io/t/photon-vbat-supercap-circuit/12390/44)) [vbat] The super cap will be a 1.5F 5.5V [cheapie from eBay](http://www.ebay.com/itm/251654325926). The [STM32F205 datasheet](http://www.st.com/web/en/resource/technical/document/datasheet/CD00237391.pdf) gives limits for VBAT operating voltage of Min 1.65V, Max 3.6V (p. 71) so that means the cap must…

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