So much has changed over the past 5 years with availability, quality, and cost of lithium batteries and pure sine wave inverters. Home Depot has been selling a heavy duty, expandable 40 volt RYOBI elec. weed wacker, 40 volt 4 amp lithium battery, and charger combo, all for $139.00. The RYOBI 300 watt Power Source inverter is $79.00. The whole package is less than that old lithium motorcycle battery was. Also, I did note from doing a little homework on Mike's post how the prices on pure sine inverters have dropped. My two 35 amp UB1 lead acid batts may be tasked with audio duty, too. But, the RYOBI combo is the best rig I have found for pumping bass into the mix when off grid.