Is it just lost in thin air? Lost as heat even though the device is not used? Thank you for the insight.
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Yeah passively rechargeable batteries loose charge as it is very slowly transferred to the air, it’s a bad conductor but it can still do it. Heat is only produced when the transfer is inefficient so the heat transfer passively is negligible. Chemical batteries slowly decay becoming less and less effective when not used.
In general in nature/physics, things tend to level out. A pile of bricks will fall down, never spontaneously assemble itself, iron will rust. This is known as entropy, broadly speaking. Things tending towards their state of least energy.
This happens by all kinds of mechanisms, but is universal. A charged battery is in a higher energy state than an uncharged pile of chemicals, so will inevitably tend towards the lower energy state. This may be a slow degradation of the chemicals inside, a tiny leak, even a slow discharge through the insulators between the two parts of the battery cell (no insulator is absolute, but some are much better than others).
Many electronic devices also use “quiescent current” – they have a super low power mode, but stay alive – just – to monitor their own battery health for instance. They use microamps, but that’s still power being used.
Let’s just look at a battery, normally you discharge them by electrons moving from the cathode to the anode of the battery outside it and positive ions moving from the anode to the cathode internally in the battery.
But batteries are not perfect the election can move internally too but at a quite slow rate. The result is the same as if you connect a resistor to the battery, the energy is converted to heat. A slightly warmer battery than the surrounding will lose heat to it just like any other warm object.
In an electronic device, there is another way it can happen. Lots of devices are not totally off but in a low energy usage state. The power button on a phone does not connect and disconnect the battery, it just creates a connection an electronic part that is always on can detect.
If you have removable batteries in a device then remove them to make them last longer. It also stops a battery that fails and leek from damaging the device.
A halfway option is to add a bit of insulation so the battery is in the device but not the connecter, a piece of paper or plastic work fine. It also stops them from being accidentally turned on in for example a bag. If you ever have purchased an electronic device you have to pull a tab out to make them work this was done at the factory.
So the device using a bit of energy all the time can be the explanation too.
>where does the lost energy from the previous charge “go”?
A battery’s “charge” is physically the proportion of chemicals in their non-reacted state to the reacted state.
Your typical alkaline battery uses zinc and manganese dioxide as their reactants. These are slowly converted to zinc oxide and manganese trioxide, and electrons flow through the circuit. They can’t react directly because of the internal structure of the battery keeps them apart.
This structure isn’t perfect, though, and some leakage happens. This is called self-discharge, and it’s why batteries lose charge even if they’re not being used.
>Is it just lost in thin air?
Sort of.
>Lost as heat even though the device is not used?
Yes.
The same thing (as in, the same chamical reactions) happens as when it discharges normally, but no useful work is done. It’s just pure heat, poof, gone.
It’s because a rechargeable battery which is disconnected at the contacts is still connected internally. It’s usually insulating enough compared to the metal wire connection not to make a difference in normal operation, but it can still internally discharge over time. And depending on the device, it might not be really “switched off” and still leak current through the electronics.
Depending on the construction, non-rechargeable may or may not have that issue. But it will still take a long time and the manufacturer would include ot in the shelf life if it occurs.
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