Just a thought... instead of using an ESP, what about a $10.00 Pi Zero-W and install a "local Blynk server" on it. Turn the Zero-W into a hot-spot and use the Blynk App to control the gate. You can even add a button (home screen App) to your smart phone home screen and not even open the App to control the gate. Have it send data back to your smart phone with the charge left in your battery.
Just a quick search on Blynk and I found this post, https://community.blynk.cc/t/setup-pi-zero-w-as-ultra-portable-server-and-ap-tutorial/12411 , You can search Blynk Community for more post, Blynk has a very good community to help you set it up...