Sifus, I'm looking for a budget smartphone, RM700 max. I'm looking for one with following strong points:
1. Long battery life
2. Not too big, around the size of iPhone 4.
3. Good performance at normal use. E.g. Not laggy when swiping through homepages.
4. Good for basic use like running chatting apps. Gaming and video watching is low priority.

After a bit of researching, found the following close to my needs.

1. Nokia Lumia 520 - Nice design with free offline GPS for one country.
2. Nokia Lumia 620 - Design is better than Lumia 520, free offline GPS for global use. But poorer battery life compare to Lumia 520.
3. Huawei Ascend G510 - Longest battery life of the bunch. But also biggest and most expensive of the lot.

All info obtain from reviews.

Any other recommendation? Or anything bad about my three choices?

Thanks. But is there really a way to upgrade Lumia 620 battery?? I can't find any info online.