Which Windows phone is better, the Nokia Lumia 625 or 520? Regarding the price and performance/battery, which one should I get?

Update. I bought the Lumia 920, and I am very happy with it. The battery life is cool, makes it the whole day with some gaming and nav. It goes for 22 hours of random use, and still 7-10% remains (2 hours app). So, to make it worth to other people if they read this, it is a go! We need more people using wp and also more reviewers for apps in the store as there are lots of apps unreviewed, that are free and excellent. From a previous HTC one X user (that switched to windows because of sheer boredom with android). Wp has some issues, not so common and heavy bugs, but it gets better day by day. I would say switching from android to wp, is like going from windows to linux. Peace.

I've got those two phones in addition to my daily driver. First and foremost, the numbers on the Lumia line matter; the lower the number the lesser the hardware capabilities. Both the 600 and 500 line models  are budget models; are you sure you want to step down to a budget phone? Second, the battery performance on all of the Lumia family is about the same...  what matters is the capacity of that battery and what capabilities you use on a regular basis. The greediest power consumers are (in this approximate order) the GPS, screen, cellular radio, Wi-Fi radio, and Bluetooth radio. Having said that, the scenario you stated will certainly make it through the day without charging... as long as you understand that your biggest drains are going to be the gaming and navigation. Navigation is particularly dastardly on that point; it's one of the few things allowed to run all then time. And I do mean all the time; you'll want to manually edit out of that app if you're not using it. That's simple to do though. Gaming can be a drain because it requires constant heavy CPU processing and must other apps don't. Everything else in this answer are reasons why you should buy the 620. Third, there is a significant difference between the screens on those two phones. However, you won't really notice a difference between the 620 and higher end phones unless you compare them side by side They did a really good job on that. You can go here to compare the models: http://www.nokia.com/us-en/phones/all/ . Be aware that you'll want to look at the full source to really see how they differ. Long story short, there is a significant difference in their capabilities. Most notably the processor, screen,  and location sensors. Also the 520 models do *not* have a camera flash, a front-facing camera or NFC. I hope this helps!