The most numerous TeV sources in the Milky Way are pulsar wind nebulae (PWNe); giant plasma clouds built up from the outflow of pulsars after stellar death. All PWNe observed with the H.E.S.S. I array have been reanalysed in the context of the H.E.S.S. Galactic Plane Survey data release. This allowed for a comprehensive population study to shed light on the evolutionary sequence of PWNe during the first 105 years after the birth of the pulsar. A prototypical example of a middle-aged PWN is the very extended HESS J1825-137. It has been observed with the H.E.S.S. II array, leading to a lower energy threshold and, in combination with previous observations, substantially increased datasets. We can therefore present new spectral studies and unprecedentedly rich images that map out the out flow process of the shocked particle wind. The data also gave rise to a new study of its neighboring source HESS J1826-130, which is one of the hardest spectrum sources in the Galaxy.