Dear Nayeli,
The battery roundtrip efficiency in SAM is an output rather than an input to the model. You can use it as an indication of how much the battery is used, and how well the system is designed. You do not need to provide a value of the battery roundtrip efficency as an input. You could compare the SAM output value to the manufacturer's value as an indication of whether the battery as modeled is performing within the manufacturer's specifications.
The conversion efficiency inputs in the Power Converters group on the Battery Storage page are intended to account for losses in power electronics in the battery storage system, not for losses in the battery cells themselves. SAM does not have a detailed model of the DC/AC, AC/DC, and DC/DC conversion process. For example, to model AC to DC conversion, it simply multiplies the AC power value by the conversion efficiency.
The default values of the conversion efficiency inputs do not depend on the battery chemistry. You can change them from the default values to reflect the expected performance of electronics in your system design.
The battery ancillary equipment losses cannot be specified as percentages. Remember that there are also loss inputs on the Losses page that you could use to account for losses in the entire system as a percentage of incident irradiance, DC power output of the PV array, or AC power output of the inverter.
Best regards,
Paul.
