# Expansion Bay Developer Program **URL:** \ **Category:** Expansion Bay\ **Created:** [August 11, 2023, 5:49pm UTC](https://community.frame.work/t/expansion-bay-developer-program/35268 "2023-08-11T17:49:39Z")\ **Posts on this page:** 1\ **Showing post:** 9
**Author:** ![Aaron\_Baff](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@Aaron\_Baff](https://community.frame.work/u/Aaron_Baff)\ **Post date:** [February 7, 2024, 11:00pm UTC](https://community.frame.work/t/expansion-bay-developer-program/35268/9 "2024-02-07T23:00:09Z")
Hm, looked at the pinout a bit, [https://github.com/FrameworkComputer/ExpansionBay/tree/main/Electrical](https://github.com/FrameworkComputer/ExpansionBay/tree/main/Electrical), looks like VADP\_GPU is needed for providing power back to the system. Haven’t looked at much else yet, but if I’m reading it right, for a Expansion Bay battery pack, you don’t need it specially regulated, between 7.6v and 20v? Or you need it regulated to 7.6v _or_ 20v? Likewise, 6 pins, so maximum of 90W at 20v (0.75a each)? So if it’s a 4s battery, for example, we can simply connect (through for example a MOSFET to enable/disable) those to the 6 VADP\_GPU pins, so 16.8v-12v (charged to discharged) would be just fine? Or do we need to do constant voltage 7.6v or 20v? And looks like pins 59-61 would be ideally implemented, for the EC to talk to any battery expansion bay. Is there any documentation for the EC of what exact protocol/specs an external battery should talk? And pin 63 to control if it should discharge, or charge from VSYS\_GPU pins, right? So if high, discharge, if low, connect to VSYS\_GPU to charge? --- _[View the full topic](https://community.frame.work/t/expansion-bay-developer-program/35268)._