It is a good thing that you mentioned infinix because infinix has juust released a new phone in the hot series and it really packs one hell of battery. The most powerful battery I hae ever seen so far on any phone if not phones made by energizer. This phone is not a low end. It is even stronger than tecno camon x going for 17k. For only 12k you get 3GB ram, 32GB internal storage, !4mp camera back and 8mp front. The best part is the 500mah battery. Trust me, no phone has got this much battery power.Forget fake chinese phones. This is the real deal for those who want to go digital for a low price. You can get it from Jumia or Kilimal. If you want to get it from infinix stores then get rady to travel.
You forgot to mention another very important aspect; the processor. Simu ikiwa na 50000 mAh battery na iko na mediatek processor then a 3000 mAh battery phone with a Snapdragon 675-855 will perform better than it. Also, the screen should be another important aspect.