In general your home storage works similar to the battery of a mobile phone or notebook. When there is enough solar energy available, the storage is charged. If no solar energy is available anymore, the storage is discharged and the energy can be consumed as needed.

There are two different topologies for integrating a storage into your home grid.
DC-Coupled The battery is integrated on the DC side of the system. Either a hybrid inverter or a charging controller can be used as battery interface. The advantage of this topology is a slightly increased efficiency, since the number of lossy converter stages is reduced. However, a DC-coupled system cannot be easily integrated into an existing PV-system.
AC-Coupled In an AC-coupled system the battery is integrated on the grid side of the inverter. Therefore, the battery system needs its own inverter. In contrast to the DC-coupled system, this system can be integrated directly into already existing systems. Additionally, a measurement point is required at the grid connection node. This power meter is used to determine the difference between grid supply and available solar power. Thus, it can be ensured that your battery is charged primarily by your solar plant.

In a battery storage electrical energy is converted into chemical energy. For this purpose two electrodes of different metals are connected to each other via an electrolyte-impregnated membrane. If an external circuit is connected to the electrodes, an exchange of charges through the membrane is possible. Thus, chemically stored energy is converted into electrical energy. In a battery storage system this process is reversible. This means that the power which is feeded into the battery changes the direction of charge flow through the membrane and the battery is charged.

Depending on which material is used for the electrodes, different types of battery cells are available. A well-known example are lead-acid batteries with lead as electrode material in cars. In the field of home storage systems, lithium-based cell types are mainly used today. Common types are lithium-nickel-manganese-cobalt-oxid (NMC), lithium-nickel-cobalt-aluminum-oxid (NCA) or lithium-iron-phosphate (LiFePO / LFP). Due to its safe handling and operating characteristics LiFePO based batteries are the majority of home storage systems. The drawback of this cell type is a lower power density compared to NMC or NCA which results in larger and heavier battery blocks. Therefore, some manufacturers have focussed on lithium-NMC and NCA tech­nologies.

Compared to conventional lead-acid batteries, lithium-based batteries always require a battery management system for charging and discharging. Otherwise, unbalanced charging of the individual battery cells will irreparably damage them. Also a discharge below the cut-off voltage of the battery cells have to be avoided. These safety mechanisms lead to a standby con­sumption of the storage even when neither charging nor discharging is in progress. For the selection of the suitable battery system the standby consumption also should be con­sidered.

The charging and discharging cycles as well as the aging over time are the main influences on the service life of the battery storage. Cyclic aging is mainly caused by high charging and discharging currents. Aging over time is accelerated by high temperatures of the cells and long periods of high charging levels. Therefore, the primary focus on the number of cycles to predict the durability of a battery is only of limited relevance.

The nominal life expectancy, which is specified by the manufacturers, is related to a remaining capacity of 60 % - 80 %. Hence, the storage is not defect after the reated life expectancy, but only has 20 % - 40 % less capacity. A further operation is still possible without any problems.