A decalcifying apparatus configured to decalcify an aqueous liquid, wherein the decalcifying apparatus comprises: - a DC power supply configured to convert AC power from an external AC power source into DC power; - a battery unit comprising a rechargeable battery; - an electrosorption cell unit comprising a treatment section for said aqueous liquid, wherein the treatment section comprises (a) a first electrosorption electrode arrangement comprising a first electrosorption electrode, (b) a second electrosorption electrode arrangement comprising a second electrosorption electrode, and (c) a first treatment section opening for introduction of the aqueous liquid; wherein the decalcifying apparatus is configured to operate during part of its operation time in: one part of a purification stage wherein a first DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the DC power supply and the rechargeable battery unit is charged via the DC power supply; another part of a purification stage, wherein said first DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the DC power supply and the rechargeable battery, such that the rechargeable battery unit provides part of the electrical current for purification to provide a power surge; and a regeneration stage, wherein a second DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the rechargeable battery, wherein the second DC potential difference has a sign opposite of the first DC potential difference. - a DC power supply configured to convert AC power from an external AC power source into DC power; - a battery unit comprising a rechargeable battery; - an electrosorption cell unit comprising a treatment section for said aqueous liquid, wherein the treatment section comprises (a) a first electrosorption electrode arrangement comprising a first electrosorption electrode, (b) a second electrosorption electrode arrangement comprising a second electrosorption electrode, and (c) a first treatment section opening for introduction of the aqueous liquid; wherein the decalcifying apparatus is configured to operate during part of its operation time in: one part of a purification stage wherein a first DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the DC power supply and the rechargeable battery unit is charged via the DC power supply; another part of a purification stage, wherein said first DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the DC power supply and the rechargeable battery, such that the rechargeable battery unit provides part of the electrical current for purification to provide a power surge; and a regeneration stage, wherein a second DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the rechargeable battery, wherein the second DC potential difference has a sign opposite of the first DC potential difference. one part of a purification stage wherein a first DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the DC power supply and the rechargeable battery unit is charged via the DC power supply; another part of a purification stage, wherein said first DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the DC power supply and the rechargeable battery, such that the rechargeable battery unit provides part of the electrical current for purification to provide a power surge; and a regeneration stage, wherein a second DC potential difference between the first electrosorption electrode and the second electrosorption electrode is applied using the rechargeable battery, wherein the second DC potential difference has a sign opposite of the first DC potential difference.