Small size and portable vs. power for outages that last more than a few days may represent attributes that cannot be reconciled. I live in hurricane alley and have toyed with various options. By far the simplest, most dependable, and most robust for power delivery is an easily obtainable 12 volt 7.2ah SLA battery carried in something like this. It is a bit heavy, but it is very portable. Simply add the 12 volt cell phone vehicle charger of your choice and charge away -- for a long, long time. SLA batteries have low self-discharge, have a long useful life, and are relatively easy to charge. When the battery finally dies(a few years if cared for properly), just replace it with another one.