Just get into the habit of plugging it in before you go to bed, if you can't get it to work less.
Make sure it is not set to continually link up to the internet for e-mails, weather conditions, etc.
On all the smart phones I've seen, you can pull down a kind of "blind" over the screen for a quick check of settings. Without even pulling down this helpful menu, you can see in the bar at the top what is actually activated at any given time.
Make sure that none of the following are switched on unless you are actually using them:
Bluetooth
Wifi
GPS
(Data traffic).
When abroad, it's best to switch off data traffic, even if you do decide to have it on whilst in your home country. I usually have it switched when in the UK because I have an agreement with my provider that I can use it for €2.99 a day, but at my mother's house I have little or no signal, so I can't use it enough to make the cost worth it. To prevent automatic linkups with the net, it's very easy to switch off the connection for 24 hours.
You can still make phone calls and send texts with that switched off, but Whatsapp won't work, of course.