Mains Or Batteries

[nailit]

if you plug a radio (or any other battery operated appliance for that matter) in to the mains while batteries are still in it, would it be using the electric or the battery to operate?
I ask because I keep a radio at the side of my bed and like to listen to a bit of 'chat' before I go to sleep, but have recently realised that my plugged in radio also had batteries in but when disconnected from the mains the batteries were dead. Would have thought that the mains would have overridden the battery.
Thanks.

[Buenchico]

I've had dozens of mains/battery devices over the years and plugging in the mains power cable has always disconnected the batteries. With older devices it was a physical microswitch (operated when the cable was inserted) that disconnected the battery circuit. With newer devices it's probably lore likely that there's circuitry detecting power entering from an external source.

If, say, the switch on a mains plug has been left 'off', or the fuse in the plug has blown, you could then end up believing that you were using mains power when, in fact, the device was taking power from its batteries.

Or, of course,it could just be a coincidence that the batteries are now flat. (Some types of batteries only have quite short shelf lives, so they can still go flat even when they've not been used).

[Togo]

nails, some appliances do not incorporate a circuit to charge a set of, or a laptop type battery. I suspect your radio has a compartment to fit a set of the HP11 or HP2 type batteries that you find in say a hand held torch or flashlight. These will run down in time even though you are not drawing power from them when using the mains lead.

[nailit]

Thanks Buen and Togo for quick replies. Yes, it was cheap batteries in the radio so that all makes sense.
Thanks again.