Don't let the terminology of cell vs battery be confusing. A battery can be a single cell, or a group of single cells connected in either parallell or series. If you connect two 1.2 volt cells in series, the total voltage is 2.4 volts. If you connect them in parallel, the voltage is still just 1.2 volts...but they will "last" twice as long. Examples of a single cell could be an AA alkaline, NiMH or NiCd. When we place those cells in a battery compartment, they become the battery. Individually, however, they are simply cells within that battery. As an example, if you had a flashlight that took two AA cells, those two AA cells are the battery. If you had a flashlight that took only one AA cell, that one AA cell is the battery.
To answer your question "would my 2,500 mAH or 2.5 amp per hour 1.2v batteries x8 last just as long or longer than the stock rechargeable "battery"........I doubt it, because of the maximim capacity of the initial "full" charge. What I have seen is that the Li-Ion pack and AA alkalines will allow the battery icon to show a full charge. From my limited experience using NiCd or NiMH cell packs, they do not. That would indicate to me that the "meter" that controls the number of bars in the battery indicator is capable of measuring 12 volts. Since we know the 8 AA alkalines total 12 volts, that seems logical. Since the NiMH and NiCd batteries only allow for a full charge of 9.6 volts, it won't fill up the bars in the indicator, even when fully charged. Lithium Ion batteries are a different breed of cat. I don't know how many cells are used to make up the LI-Ion pack in the CTX3030. I would guess it is three, based on the battery indicator showing a full charge with the Li-Ion and AA alkalines. And, a Lithium-ion is charged at approximately 4.2 volts......+/- 0.05 volts. This would indicate that a fully charged Li-Ion Battery pack would be at about 12.6 volts. But again, with the voltage regulator, this slightly higher voltage is irrelevant. In addition, NiMH cells each having 1.2 volts doesn't mean the detector is pushing electrons at a voltage of 9.6 volts. It just means that there are 9.6 volts available to push those electrons. Again, the voltage regulator "limits" the amount of voltage put to use. If someone felt compelled to take it apart to measure the current flow through the electronics, we could learn how many milliamps the CTX 3030 requires. If we knew that, along with the resistance of the electronics, we could mathematically figure out how much voltage is required to push those electrons through the detector. JMHO HH Randy