Buy used, can get more amp for less money, example
DC 3.5k $500
http://www.stevemeadedesigns.com/board/topic/205259-dc-35k-dc-lvl4-xs/
DC 5.0k $800
http://www.stevemeadedesigns.com/board/topic/205465-dc-audio-5k-smd-18-v1-xs-power-d3100-for-sale/
Was shocked to see it charge up this high after 24hrs, the others battery I've done had a higher resting volatge and took lot longer to get to this point..