Okay, now let’s look at little of the science behind batteries, starting with your typical alkaline battery.  Believe it or not, batteries have a shelf life. This is because they use chemical reactions to create the electrical charge and that chemical reaction only lasts for so long, even if the batteries are never used. Batteries are also temperature sensitive. This is once again because of chemical reactions, and those reactions are temperature sensitive. Cold batteries do not perform well and hot batteries lose charge at a faster rate, even when not being used. Basically, batteries do not like temperature extremes, and both extremes reduce shelf life and overall life of the battery. Therefore, just because a battery is new does not guarantee it has full current capacity, or, in layman terms it does not guarantee the battery is full. Batteries stored in temperature extremes, such as the majority of warehouses across the U.S.A. experience during the extreme seasons, will inevitably have their capacity affected.

Rechargeable batteries have even greater issues because they involve a charger circuit that can only make a calculated guess as to level of charge the battery is at during the entire charging process.  What these circuits do to measure this is to look at the internal resistance of the battery, which changes as the battery charges.  Batteries with little or no charge have a lower resistance, while those that are closer to fully charged have a higher internal resistance.  But temperature changes this internal resistance as well, which is why cold batteries charge at a slower rate.  That is why a cold battery does not charge as well or as quick, because it’s internal resistance is higher.  To a charging circuit, a cold battery appears to have a higher charge than it actually does.  In this situation the battery will not be fully charged.  It will often be of the correct voltage, but the current capacity will be greatly diminished.  Batteries that are hot when charged will often suffer damage because the charging circuit is fooled into thinking that a batteries charge is much lower, and it will dump more current into the battery, which cause the chemical inside to degrade at a much faster rate than normal.  This will often leave a rechargeable battery in a state where the voltage looks good, but it’s ability to supply current is drastically diminished.

But there’s another issue with rechargeable batteries, mostly seen with NiCad batteries and that is charge memory.  With rechargeable batteries, if they are not properly used and recharged, they will develop what is often called charge memory, or they will actually begin to consume themselves.  Charge memory happens when a battery is used and barely drained of it’s total current capacity, and then is put back on the charger.  Because of how the chemical reaction works, the battery begins to experience a reduced capacity as the fully discharged point move higher and higher, closer to the full charge level.  In other words, since it was only discharged a quarter of the way before it was charged, it begins to see that as the bottom of it’s capacity.

With some of the Lithium Ion batteries there is another issue, which is that when they are fully discharged the battery begins to consume itself chemically.  In essence, it begins to eat itself, thus reducing it’s current capacity.

Now in all of this there arises another issue and that’s the discharge curve.  Discharge curves are a visual representation showing the voltage level of a battery over the discharge process. Lead acid batteries have a slow decline throughout the majority of the discharge process with little drop off (or knee of the curve) towards the end.  Lithium Ion batteries on the other hand (and are what’s in most devices such as camcorders, etc.) hold their voltage level for a long time and then suddenly drop off.  This dramatic drop in voltage can lead to the impression that the battery went from fully charged to suddenly being drained when that is not the case.  In fact it’s normal, but for those who are unaware of this, it can look as those an external influence, such as a ‘spirit’ was draining the battery.  mpoweruk.com has an excellent article discussing both temperature and discharge curves.  I highly suggest it to anyone who thinks battery drain is a good piece of evidence for proving the paranormal.