Are batteries still giving off energy when they're connected to something? Eg, if I switch my walkman off, but leave my batteries in, will there be less energy than before in the batteries?
yes there is a very small drain or the batteries in any appliance like that....that's why manufacturers tell you to remover the batteries if they are not to be used for a long time (along with the risk of them leaking).....as long as it'snot going to be weeks on end your going to be fine though as the loss is miniscule.
When the appliance is switched off the circuit is broken and the chemical reactions which produce the current stop. Therefore there is no drain on the batteries in that they are not converting chemical energy into electrical energy. However, other chemical reactions take place very slowly inside the battery and so they do not have an indefinite shelf life.
Some gizmos (like my little portable radio) have a tiny tiny battery on the circuit board that keeps the tuning and clock information. Even though the radio is switched off, this tiny battery is kept charged from the main batteries that you put in.
The amount of current flowing is very small, but eventually it will discharge the main batteries slightly faster than their natural shelf life.
Nimh, especially, discharge within the device. best remove your current nimh [scuse pun] and put freshly charged ones in say a camera just before usage.