If the iPad disconnects when idle (sleep/locked) you may need to verify the your WiFi Settings for each of your configured WiFi Networks - ensuring that they are set to Auto Join:
Settings > WiFi > [WiFi Network / SSID] - tap the “i” icon - set Auto-Join to ON
Unless Auto-Join is enabled, your iPad will not automatically reconnect to the WiFi network when resuming from sleep - or when coming into range of your WiFi network.
Auto-Join is enabled/disabled for each configured WiFi network.
As for your unexpectedly high battery utilisation, try a forced-restart of your iPad - as this will often clear a stalled process or isolated software issue:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.