The battery efficiency of home based battery solutions depend on multiple criteria. For example whether electricity is converted from AC to DC through a PV- and battery invertor or wether it directly stores DC from PV-panels. The set-up of your system being centralized in the neighbourhood or decentralized in all the homes also impacts the equation. But also the losses in the battery modules, and EMS systems and support components (like ventilators) should be considered when doing the math.
The actual overall efficiency obviously also depends on the chosen control strategy. If the battery system is not actively steered but still operational, the losses to every cycle of charging/uncharging are relatively high. These absolute losses remain much smaller to a situation where an active steering strategy is in place.
At Schoonschip we benchmarked the efficiency issues we identified with several other pioneering energy project and we noticed that in several projects the actual figures were much lower than previously expected. Multiple pioneering projects in The Netherlands where home battery systems have been applied for some years seem to achieve no more than 60% or 70% of efficiency for a regular control strategy such as ‘maximisation of self-consumption’. Solid analysis and optimisation might improve these figures to a certain extend.