I used my original set of Goal Zero batteries for one year with the Nomad 7 solar panel and Guide 10 Plus power bank. During that time, the fully-charged bank went from charging my 2100mAh Nexus 4 phone 80% to only charging it 10%. However, the bank was still effective at maintaining a consistent pass-through charge direct from the sun. I've tested these replacement batteries and they get me back to 80% again (at a rate of about 1% per minute if not in use). Just in time for winter nights!