It all depends on how (and how much) you use those devices.
Personally, I can say more about DSLRs than phones, and with 2 different DSLRs on 5 tours (of 2-3 weeks) there was never an identical usage so far. The "official" number of photos you can take with one battery can be exceeded by limiting every usage outside of taking the photos - those are included in the estimations. Videos and liveview are extremely draining (continuous image processing) and should be avoided if possible. Turning off the display for longer use, and taking an excessively large SD card help too (you won't waste battery deleting bad pics).
Also, with more planning and using the analog viewfinder before turning on the camera, you might save battery time while planning a shot and might skip it alltogether if it's not working out. I've noticed the amount of shots I take decreased with every tour, as I knew some shots (if taken) would get deleted anyway, which in turn reduced the number of batteries.
Always leaving the camera on would be detrimental - that might be useful for phones that need to start up a metric ton of programs each time, but cameras are rather simple in that regard. My cameras have default power saving modes that turn off the camera when not used for a minute, indicating that the manufacturer has done that math. Leaving them on for 8+ hours per day seems excessive, but you can just try that at home if you want.
Last but not least, as Jasper's answer explains, charging inefficiency wastes additional battery power. If you think your DSLR batteries are not enough, you should rather add DSLR batteries instead of carrying additional charger devices and powerbanks. Even the cheap chinese ones give you a better mileage per weight. Charging everything from the same source might be more flexible and convenient, but wastes battery (by charging inefficiency) and weight (by additional devices).