JBL offers its refurbished JBL Studio 2 Series 12" Powered Subwoofer for $199.99 with free shipping. That's $400 under the lowest price we could find for a new unit. This 300-watt speaker features:
29Hz to 150Hz frequency response
12" PolyPlas low-frequency transducer
line-level and LFE inputs
phase switch, level control, bass boost, & signal-sensing auto power
Note: A 5-year JBL warranty applies.
You very likely are putting your laptop battery into an early grave.