Built for reliable performance during extended power outages, the Dakota Lithium Home Backup Power & Energy Storage System makes going off grid easy. Important Note: This promotional offer is exclusively for customers who have already purchased the 48V Stackable ESS system and currently have a compatible inverter installed.You can stack up to four units total (48V 400Ah) with the 3kW inverter. This promotion allows you to expand your current system—add more power, not more hassle.