# Using a low current battery bank that is powered by a larger battery bank

**URL:** <https://community.sparkfun.com/t/using-a-low-current-battery-bank-that-is-powered-by-a-larger-battery-bank/44221>\
**Category:** Power\
**Created:** [July 18, 2022, 7:31pm UTC](https://community.sparkfun.com/t/using-a-low-current-battery-bank-that-is-powered-by-a-larger-battery-bank/44221 "2022-07-18T19:31:30Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![creinholt](https://avatars.discourse-cdn.com/v4/letter/c/96bed5/32.png) [@creinholt](https://community.sparkfun.com/u/creinholt)\
**Post date:** [July 18, 2022, 7:31pm UTC](https://community.sparkfun.com/t/using-a-low-current-battery-bank-that-is-powered-by-a-larger-battery-bank/44221/1 "2022-07-18T19:31:30Z")

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I have an ESP32-based project for a device intended to be outdoors unattended for around 6 days. I have used the Sparkfun Low Current Lithium Ion Battery Pack - 2.5Ah (USB) prior with other microcontroller-based projects. However, its capacity is not large enough to make the 6 days. Is it feasible to plug a larger battery bank into the charger of the low-current battery bank to extend the device’s battery life? I believe the low current battery bank has a large enough current draw for charging to keep the larger bank active. However, I fear it would be too inefficient with heat dissipation to achieve a significantly longer battery life. Should I invest in a LiPo-based solution instead?

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**Author:** ![TS-Russell](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/ts-russell/32/6092_2.png) [@TS-Russell](https://community.sparkfun.com/u/TS-Russell)\
**Post date:** [July 18, 2022, 8:31pm UTC](https://community.sparkfun.com/t/using-a-low-current-battery-bank-that-is-powered-by-a-larger-battery-bank/44221/2 "2022-07-18T20:31:00Z")

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That should work (not verified with that particular power bank, but I’ve done something similar with other ‘cheap’ ones) though I would strongly recommend switching to a LiPo like this one [https://www.sparkfun.com/products/13856](https://www.sparkfun.com/products/13856)

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**Author:** ![jremington](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/jremington/32/6595_2.png) [@jremington](https://community.sparkfun.com/u/jremington)\
**Post date:** [July 18, 2022, 11:40pm UTC](https://community.sparkfun.com/t/using-a-low-current-battery-bank-that-is-powered-by-a-larger-battery-bank/44221/3 "2022-07-18T23:40:36Z")

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> However, its capacity is not large enough to make the 6 days

Have you fully explored sleep options, both for the CPU and the sensors?

Also, that battery pack has a step up converter to produce 5V, which is then stepped down to 3.3V for the ESP32.

About **half** of the battery capacity is wasted as heat in that process. An 18650 cell with a 3.3V regulator would be significantly more efficient.