Connected Standby as a Standard is 5% drain over a 16 hour period, the SP3 uses a modified version that only uses Connected Standby for 4 hours, then moves to a "light hibernation" for 8 hours at the 12 hour mark it goes into "deep hibernation" which should hold a charge for over a year.
Some of the issues I've observed on these and other communities is as the device attempts to move from CS to hibernation it wakes up and isn't able to re-enter CS and others is a driver or application prevents the device in achieving the 90% Power Floor Target, which means that in CS the device should be at idle and the lowest power state.