I had a Xiaomi Mi 4i which had a SD615, thinking "how bad can it be". Turns out, it was painfully slow to use; no match at all to the vanilla Mi 4 with a SD801.

I had a Xiaomi Mi 4i which had a SD615, thinking "how bad can it be". Turns out, it was painfully slow to use; no match at all to the vanilla Mi 4 with a SD801. Maybe the current generation is different, but I got a Mi 5 (SD820) and haven't looked back. The battery life is fine, enough to last a full day with lots of spare capacity.