My smartphone, Huawei GR5, gradually got unstable and very unstable later.

Symptoms:

1. Sudden shutdown and reboot; especially when stating to use camera. It is very frustrating, since you lose a shutter chanece.
2. After reboot, the battery is red lamped (3%). and completely shutdown while rebooting. (reboot does not complete.) It means my smartphone becomes just dumb small box.
3. Camera focus gets even worse. Huawei GR5 camera is bad, compared to even iPhone 4. It gets even worse.

Battery seemed wrong. I had tried to find a battery for the smartphone without success. But I could find one. I opened the smartphone and change the batery. Voila, the symptoms are gone.

The new one, made by a third party, is 10% lighter than the original one.

Conclusion: it was a battery which caused all troubles.