Even if u have standard speaker with just 3.5mm jack, and access to USB power. Check this kickstarter project out:
http://tinyurl.com/8vfmwaf
if they reach the 160,000 goal, they will revise it further by making it rechargeable.
http://tinyurl.com/8vfmwaf
if they reach the 160,000 goal, they will revise it further by making it rechargeable.