On the Electron do not connect VBAT to anything! It’s internally connected to 3V3 with a 0 ohm resistor. If you connect it to ground, you’ll short out the Electron. The instructions for connecting it to other things are really more important for the Photon, which doesn’t have a battery.
By the way, make sure you’ve upgraded your Electron to 0.5.0 or later. I think there was a bug in 0.4.8 that prevented retained memory from working correctly when in SLEEP_MODE_DEEP.