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Existing models of microgeneration systems with integrated lead-acid battery storage are combined with a battery lifetime algorithm to evaluate and predict suitable sized lead-acid battery storage for onsite energy capture. Three onsite generation portfolios are considered: rooftop photovoltaic (2.5 kW), micro-wind turbine (1.5 kW) and micro combined heat and power (1 kW). With no embedded energy storage, the dwelling exports energy when the microgeneration system generates excess power leading to a high level of generated export throughout the year. The impact that the size of installed battery has on the proportion of the generated export that is reserved onsite, along with the annual energy discharged per year by the energy store is assessed. In addition, the lifetime algorithm is utilised to predict corresponding lifetimes for the different scenarios of onsite generation and storage size, with design tables developed for expected cost and weight of batteries given a predicted generated export and lifetime specification. The results can be used to indicate optimum size batteries for using storage with onsite generation for domestic applications. The model facilitates the choice of battery size to meet a particular criteria, whether that be optimising size, cost and lifetime, reducing grid export or attempting to be self-sufficient. Suitable battery sizes are found to have lifetimes of 2-4 years for high production microgeneration scenarios. However, this is also found to be highly variable, depending on chosen microgeneration scenario and battery size.