The following is a step by step guide to using the DC Charger.  The first step in the process is identifying the SOC of the stack currently. The best way to do this is to log into the battery and obtain the value on the "Home" screen.  It can also be obtained from the Inverter, but keep in mind that there is intentionally a difference between the SOC that inverter displays and the battery displays with the difference being the % reserve the the inverter withholds from the customer (usually 8%, so when the inverter says 0%, the battery is actually at 8%. When the inverter says 100%, the battery is at 100% ).  The SOC's of the existing stack and the new module don't have to match perfectly, so if you're using the Inverter SOC value, just tack on ~5% and charge the new module to that value.