There have been a few articles on this topic. Using the Amp Clamp has limitations as ambient temperatures and the Amp Clamp Battery will drift over time. Especially if you are testing over extended periods of time - overnight for instance.
I have had good results using a 0.01 or 0.1 ohm Resistor bolted in between the B- terminal & the earth cable.http://www.ebay.co.uk/itm/191687970842? ... EBIDX%3AIT
&http://www.ebay.co.uk/itm/Gold-Tone-Alu ... 1c5a9bd9d8
You can the scope the Volt Drop across the resistor on one channel and the battery voltage on another. Next create a Math Channel using ohms law to determine Current ( a stable voltage battery support unit is a good optional extra to the test)
Then it is a case of Current = Voltage / Resistance which the correctly configured Math Channel will display for you.
Here is a thread that goes into some detailtopic9482.html
Hope that helps