Macworld One low battery is annoying. Four dead batteries is a nightmare. Avoid the disaster by getting a portable power bank with the capacity and connectivity to charge four devices at once. This compact 50,000mAh power bank is a high-capacity, high-speed charger with a low price of $39.99, marked down from $59.99. Any old power bank might be able to charge your phone. What sets this one apart is how many devices it can charge at the same time and the power output. This power bank has three USB-A ports and one USB-C. For a phone, tablet, or earbuds, 30W is a lot. For a computer, it’s not ver…