If you already have a powerbank you could try something like this. You can buy the same units from Aliexpress much cheaper but you will have to wait for delivery.
Connect your power bank using this cable to provide back-up power to your router, car Air Purifier, etc USB 5V to 12V DC Jack
www.geewiz.co.za
The Huawei B315 battery pack has an output voltage of 7.4V so I would personally rather use a 5V to 9V adapter but they might be difficult to find locally.
If you are willing to wait a few weeks you could purchase a 5V to 9V or a 5V to 12V converter from Aliexpress. Shipping to SA works out to around $2. You should be able to purchase any of these units for less than $2 if you use a coupon. I can send you a referral code if you are interested.