The HF 65892 CEN-TECH Battery Analyzer actually does a good job
I consider it a good enough tool to have two of them
Works very similar to a proper capacitor ESR meter which
Sends out a high frequency (typically about 150KhZ) AC signal then reads the response through the four connections on the battery clamps. Then on to a few rather simple calculations/look ups
Nothing special Standard - Voltage measurement
Battery internal resistance - uses the four connectors on the clamps and does a good job most of the time
CCA value - a best guess but actually very close if given the proper input when doing the reading
Yes two 6VDC batteries in series can be considered a single 12Vdc battery. Even a series parallel combination of 4 or 6 or even 8 GC 6VDC batteries can be considered a single 12VDC power source. As others stated series voltages adds and current stays the same, parallel current adds and voltages stays the same.
Enjoy the new meter
Check out the "reviews" on the HF web site for the tool