Is there anything like an external power source?

I am using lenovo y450a, its performance is ok while its power loses so quickly.
from Lenovo, there is no another larger capacity battery for y450a and I don't want to buy another battery of y450a.

I remembered that there is an external power source which is mobile and it can provide a longer service hour.

Would you suggest one if they are available?

btw, I also concern about the safe in using them as Li- battery can be fatal in some cases.

Thank you for your attention.