Here are my opinions.
Firstly there is an application called "WatchDog Task Manager". You can install this application (or use the free version) and configure it so it kills processes exceeding certain thresholds. This can be set for the parameter of CPU or battery usage. This is primarily for CPU.
Another application you could configure is "SnapDragon BatteryGuru". Now this is highly opinion based, but I used this on my Samsung, HTC One M7 and M8 and noticed improved battery life. This application monitors your daily habits for battery and places certain application rules for when it syncs. This could assist in restricting FB (or even Messenger) from hogging battery.
You could also go to the extent of installing "Memory Booster" which has several additional add-ins such as task killers and battery saving technics. I would not really believe this suitable, but it is a worthy mention.
Of course there are many other applications that you could look into that apparently help boost your battery life. The key to boosting battery life is minimising applications that actively have "wakelocks". More on wakelocks can be read here: What are wakelocks?
Feel free to comment on this if I have missed anything or your disagree with this. If you believe this a sufficient and correct answer, please mark it so.