Why not get a $250 Xiaomi with Snapdragon SoC and a $50 powerbank? You’ll get a much better experience performance and updates-wise and battery might even be better due to the better SoC.
I really wouldn’t recommend Doogee or Ulefone. Anything you gain from the battery capacity (which might even be a lie!) is cancelled out by horrible kernel+OS tuning and Mediatek SoC.