An energy storage apparatus and an energy storage system. The energy storage apparatus is configured to be connected to a power conversion system, where the power conversion system is capable of cooperating with M energy storage apparatuses, a rated output power of the power conversion system is P, an energy of the energy storage apparatus is Q, a duration for the energy storage apparatus to discharge from a fully charged state to a fully discharged state is A, satisfying: 0.7≤P/(MQ/A)≤0.99. With P/(MQ/A)≤0.99, it is ensured that the power of all energy storage apparatuses cooperating with the power conversion system maintains sufficient margin relative to the power of the power conversion system, eliminating the need for capacity supplementation of the energy storage apparatus over a long period, achieving long-term reliability of the energy storage apparatus. With P/(M*Q/A)≥0.7.
