I have not used an Electron but this link may help:
https://community.particle.io/t/powering-electron-via-solar-power/30399/2
The battery you are looking at may work. However, always check the battery terminals for proper polarity BEFORE plugging into your device. Most, if not all, single cell LiPo batteries I bought thru eBay or Amazon needed modified termination to work correctly. I think the same will be true for the battery you found. Looks like the wires are reversed from what you need. But, you can fix that.
I have ordered a 12000 mAh battery from eBay but need to attach a connector and test it once received. It will be a while:
https://www.ebay.com/ipp/353458607762?transactionId=1297250576022&_trksid=p2047675.l48352