up as a power bank. this is a pretty big surface and you can place this in the sun so it will charge a lot. charging from ambient light does have its limitations, though. how about a laptop, how far away are you from being able to create that sort of power in the bag? the laptop you know is super power hungry. and a phone as well, you just are not going to get enough power? laptops and phones, you need much stronger light, or you need a larger surface. but who is going to walk around with this? it's not going to happen. so it's all about finding the balance. what is the available surface on the product, how do you normally use the product in your daily life. products like these are banister headphones do still have a back—up charging port, though, for those who just still wanted there for peace of mind.