Sometimes, one can find a faulty (low reading) battery fresh out of the package. Other times they will work for a while, then one just decides its time to quit. Using the digital meter I find it much more accurate than the meter with the sweep hand. I have found faulty batteries even showing a negative voltage. This has even shown up in rechargeables. A rechargeable in this state can be recharged, but it will take quite a bit longer than normal. When I use a charger, they will flash when charging, then come on with a solid light when charged. This does not mean that both batteries in the same section are fully charged. The charger will show this with the highest charged battery. I test all my batteries before installing in the charger and again approximately 1/2 hour after removing from the charger. My reason for testing before installing in the charger is to put a pair that has a closely matched reading in the same section of the charger. Testing the batteries after about a 1/2 hour after removal gives the battery voltage time to stabilize, resulting in a lower reading than fresh off the charger. I find this really shows up when charging a vehicle battery.
As for weather temperatures, any battery will not put out as good when the weather gets colder. This is where the Ultimate Lithium shine, due to there higher voltage reading (1.79 to 1.83 volt fresh out of the package). Copper Top Duracell are another good battery testing 1.60 volt. The rechargeables are useless in the newer cameras. When battery voltage drops to 1.30 to 1.38 range, the newer cameras start to malfunction or fail all together. This voltage is usually tops for most rechargeable batteries (2.2 volt on the package, but most can be bumped up to around 1.38 with a charger).
You mentioned finding the "D" batteries better. I agree with you there. The "D" has more storage capacity than "C" or "AA". As an example, your vehicle comes with say a 650 cold cranking amp battery. You change that out for a higher cold cranking amp battery (750 or 850) your vehicle has much more cranking power when starting in cold weather.