WiFi drastically drains the battery. There is a setting to disable WiFi while the phone is on sleep. However, it's all or nothing: either you are connected all the time (and kiss good-bye to the battery) or you receive notifications from WhatsApp only when you happen to turn on your phone, maybe next week.
Is there an app that would force the phone to connect to WiFi every, say, 10 minutes while on sleep, for WhatsApp to check for new messages? This would both save the battery and permit receiving messages (almost) in real time.
As a workaround, maybe the app could just wake up the phone every 10 minutes, though this is a bad solution.
Preferably I would like a ready app, not a programming way of doing it -- I am not good at programming for Android.