Hi, I’m an Electronic Test Engineer , I’m 59yrs old so I’ve been playing with this stuff for many years. The question as to whether you should keep your radio on continuously or not requires reliability testing to honestly answer this question . It is extremely specific right down to the production run. Many components inside the radio have mean time failure ratings. There are always alternative parts sources used during the production cycle. So not even all the radios may have the same components but similar from different manufacturers. There are almost always ECO’s Engineering change orders that are changes so different sn”s may have different revisions inside. Some to reduce cost. Some to increase reliability, The company more than anything wants no returns caused by production errors or design faults during the warrantee period. This could destroy every dime of profit. Also safety is important so they have been paying closer attention fire hazards like the input transformer on the external power supply. But they are not likely to use parts even resistors with low mean time failure because this can significantly increase expense. But I must admit I find electronic components designed made in Japan are high quality. The problem is, you can’t really know where it is all made. So the best thing is consider the manufacturers record for quality. And search for reliability reviews on the specific product.
Does turning the radio on and off reduce the products life? Sorry but the answer is similar. The unit has a power up sequence, it’s out of your control and in the design. So turning the unit on an off in succession is a very bad idea. But wait for the internal components to normalize after you shut it off. At least 30 seconds. Inrush current depends on the ability of the dc supply to provide it and whether there is a soft start circuitry installed. In low power equipment like a scanner internal capacitance is small so inrush in small. But the input power supplies are poorly regulated so initial voltage maybe higher than is healthy. It depends on whether there is zener diode protection inside and what values are selected.
Based on my personal experience I would shut it off when not in use. If I’m going to use it 3 or 4 times in a 6 hr period keep it on. Do not keep it off for an extended period of time. After six months or more capacitors have a habit of exhibiting high leakage on initial turn on. This is not healthy. After a few years it is best to bring it slowly on a variac. Older radios using incandescent back lighting tend to fail. Led’slast much longer. Low voltage capacitors 5 to 35 volts are not likely to have this problem. So your scanner or portable radio is not inclined to have inrush failures even when turned off for extended periods. High voltage large electrolytic capacitors should be reformed (charged up on slowly).
I recommend against using a timer externally to turn your radio on and off. Always use the on/off switch. It’s not the same.
A general rule of thumb is to leave High Power,Tube equipment or High Voltage devices on or on standby. Low power . low voltage Semiconductor equipment should off except when not in use . But use common sense. If you are going to use a few times over 4 hrs leave it on, going to bed turn it off.