I apologise for the delay in reply.
The Cloud does not log when the Bolt is only, but what you can do is make a product on the Bolt Cloud which will monitor a certain pin on the Bolt.
in the code section, just plot the data from the pin.
Once you link your Bolt to this product, the Bolt will send the pin status every 5 minutes to the cloud. When the Bolt is powered down, it will not send this pin status, which will effectively be the time at which the battery completely powered down.
Also as a side note, what you can do is have the product monitor the A0 pin, and connect the power pack to the A0 pin of the Bolt using a voltage divider configuration. This will tell you what voltage the battery pack was at, at what point in time.