A good example is an AM-FM battery radio. If you listen to AM the
battery life if higher than if you listen to FM only.
The first symptom of weakening batteries is distorted FM, good AM.
This is due mostly to the audio out demanding more power to cover the FM audio band width. As the bats get weaker AM gets drifty etc. If
you listen at VERY low volume symptoms are reduced.
I dont know what they are called but there are power packs that can
get around this, rechargeable bigger batteries. You can wear them.
I never used one but a lot of metal detector hobbyists use them to
run there machines for days....
73 Zeno
LFOD !