Minecraft wiki entry for Minecarts, associated text: A minecart with no rider, at full speed, can climb 10 blocks on unpowered, upward sloping rail. This suggests that powered track is needed at this height only to keep a cart climbing. However, the cart slows so much that it can reach only another 5 blocks high with 2 lengths of powered track starting at 9 blocks high. Further testing showed the minimum number of powered blocks to keep the cart climbing well is 3 powered rails every 6 blocks starting at 9 blocks high, at the cost of a strong reduction in speed. To maintain speed in a climb a ratio of 5:4, powered versus regular rail segments, is a good compromise for decent speed at a reasonable cost, starting with 2 powered rails on the flat before the upward slope to be sure the cart starts the climb at maximum speed.