Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Error E05 matches what you have described: it means the internal battery is at a low level (or if it is not defective, it is nearly discharged.)
Depending upon whether the PowerHub merely needs to be supplied more power, and also upon whether it is still new enough to be within warranty coverage, it either needs:
1. to be supplied with more power to charge up the internal battery, or,
if it is at least 1 1/3 years old,
2. it needs to be serviced, to have the internal battery replaced, perhaps, owing to the fact that rechargeable batteries do eventually fail... though lead-acid batteries may have other problems than simply 'failed', other technologies of rechargeable do fail, period, after a period of at least 1 1/2 years roughly.
So I recommend considering whether it is new enough to be covered by warranty before opening its case (since opening the case voids the warranty coverage) and then if it isn't, examining the battery, and its connections, and considering whether it is likely to be the battery, the connections, or the charger circuits, that are at fault. It is surely one of those, I think, with an E05 Battery Low error showing on it.
If this answers your question, please rate my answer. A five-star rating would be appreciated!
If you need more info, for instance as to whether to get a replacement battery, or if you have any comments, use Reply To Expert to respond.