I've use 2300mah rechargeable batteries, which I recharge externally, but I do plug in the power cable when running discovery mode at night. I've ran the batteries bone dry to where the unit won't even turn on. I've also used the power cable plugged in for over 24hrs straight. I have never had a clock issue EXCEPT when adjusting for DST. Which I just learned is part of your Sentinel profile so unless you read from scanner first, it will default to the profile that is on your pc.
Although my unit does not do very well on the rechargeables (longer to charge than to use), it never seems to lose time. But again I purchased it new and from earlier posts someone said it was used? Maybe I got lost in the thread
Make sure firmware is updated and the clock is set how you want it in the software BEFORE you write to scanner. Or read from scanner, save it, then make adjustments and write back to scanner. That silly little issue messed me up for days.