There is a recent market trend towards industrial battery powered products that demand occasionally very high discharge rates. This fact is today solved by oversizing the battery or by using more expensive high power nickel-cadmium batteries. Within an EC funded project, ultra high power lead-acid batteries for UPS applications are being developed. The batteries are characterised by a thin electrode design linked to the use of novel separator materials to increase the battery life under floating and deep cycling conditions. Battery performance under different working conditions is presented, in comparison to standard products, and the battery improvements and failure mechanisms are also discussed.