I didn't have Write In Chat button at first, but now I don't have Invite to Battle button.
It's because of update not my device, since my computer is not lagging and fresh.
Can you please be more specific? Show us screenshots, please.
"Write in Chat" button is only available in server chat and "Invite to battle" button is visible in Friends system, and only if your friend's rank meets the rank requirements of the battle.
Customer support service by UserEcho