First we can say that, power bank is not depends on mh power. it depends on brands and good quality product.
some brands like apple, sony, lenovo like that which is good but in market selling different types of power bank which contain more hp power.but actual it is not working which is given.in market found in high MH power bank selling but it not works.i think apple or soney power bank is more perfect, because a good power bank protect to mobile phones from hardware shocking.i am using soney power bank which is used in previous 2 year but no defect found.
safety for power bank is different rule like that.
1)power bank is full charged and not to be charged again until fully dead.
2) safety for power bank keep it normal temperature.
3)time to time cleaning without any liquid material.
so, guys I think, you happy my review.