My J7 Prime has KNOX feature in build and a led indicator which is useful if office. As my data and privacy is more secure and I do not have wake up the screen every time to check notifications. Also both the device comes in metal build, but in different design.
So, my final advice, If you wait for few weeks than compare the J7 Prime(2017) and A7(2017); than buy the one. And if you don’t want to wait for few weeks. Than choose A7 if you have the budget and looking for better cameras to capture images and screen to enjoy multimedia including the VR videos. But J7 is also good if you have lower budget, want the KNOX feature and that small blinking LED indicator, and do not care about the VR videos.
Final words. Before buying please take a demo of both the devices in a nearby shop, specially the VR experience in A7 and than take the final decision.
Respect and regards.
My battery backup in J7 Prime is superb. I only charge the battery at dinner time. Otherwise I do not have to think about it. It last more than my On 7 Prime and papa’s A5(2016). But I use it mainly for calls, messages, emails and social media. No gaming yet, but little media like playing songs or watching videos. Overall I am happy with the battery life. Also please remember I am using a true 4G SIM with VoLTE.
As you have said your battery is draining fast. Than please check the "Battery Usage", may be some apps are running in background. And please do not use mobile data and wifi at same time. they will eat up your battery. Last thing is get updates for your device regularly. It improves the device.