A power efficient biomedical electro-stimulator circuit BSC is provided. The circuit BSC includes a charging circuit arranged to control charging of a storage capacitor C based on electric energy from an energy source ES, e.g. a battery. The charging circuit includes an energy converter EC that applies a charging current I to the storage capacitor C, this charging current I being substantially constant over a charging period T, thereby providing a power efficient charging. In preferred embodiments, the energy converter EC is an inductive energy converter, e.g. a DC-DC converter, with a control circuit serving to provide an almost constant charging current during the charging period. In another embodiment, the energy converter EC is an energy converter that charges the storage capacitor via a series resonator, e.g. a series connection of an inductor and a capacitor. The proposed biomedical electro-stimulator circuit is advantageous for devices such as pacemakers, and neural stimulation etc. which can benefit of increased battery lifetime due to an efficient charging scheme.