Wondering if anyone experienced this before? I am using the battery pack for my 5Ds. Since I was not able to recharge my batteries in the field, I opted to use DURACELL batteries instead. Since this is the first time I am using it, I did not know what to expect, however, I was surprised to learn that the battery pack drains the batteries so fast, 6 cells in just one day use with a couple of hundred photos TOP! Not sure if this is expected? Please note, granted the condition at Yellowstone was rather cold, especially at night.
That sounds about right because alkaline cells will not deliver anywhere close to their rated capacity in service with high peak drain like your DSLR.
The current capacity of the various "dry cell" chemistry makeup has long been rated in capacity using a very slow discharge metric. So a typical 2.5 AH alkaline AA cell will only achieve its 2.5A (2500 mil) rating when discharged at not greater than 50 mils and as the current load increases the total available capacity is rapidly reduced.
Part of this is due to the less than optimal chemical reaction at increased discharge rate and part is due to the internal resistance of the cell causing greater voltage drop at high discharge rate. The rechargeable pack is much better suited for the type of high drain scenario seen with a DSLR and even more so with a mirrorless and its much greater current appetite.
For this type of service, primary cells are better viewed as an emergency rather than reasonable use power source.