I wanted to mention that I have numerous mobile radios in my 2009 Ford Crown Victoria Police Interceptor purchased from a dealer in 2013. All the radios were professionally mounted, wired, and antennas connected to NMO mounts drilled into the roof and trunk lid. I had most of the radios connected to +13.9VDC (or should I say +12 volts DC) with relays to kill the voltage when the ignition key is turned off. Four of the radios, all Motorola:
110 Watt UHF Astro Spectra
110 Watt VHF Astro Spectra
45 Watt VHF XPR4550 DMR/Analog
40 Watt UHF XPR4550 DMR/Analog
.....were wired directly to the battery and grounded appropriately to a common ground bus.
Here's what happened until recently. I went through four replacement batteries over a period of six years. Two of them were Optima yellow-top heavy-duty batteries, and the other two were the highest amperage extra heavy-duty DuraLast (Auto-Zone's branded store batteries). I had a 3 amp trickle charger attached to the battery when parked in my garage, so the voltage would be constant and fully charged (or what I believed to be). My mechanic changed the batteries when my car failed to start, even with the "floating" charger attached whenever the car was parked in my garage.
In October of 2020, the mechanic/installer discovered that even though all the radios were turned off, I had a constant drain of approximately 1.5 to 2.0 amps when the car was not running. There was no reason why that should be, as the car's computer didn't pull anywhere that amount of amperage when the car was off. To make a very long story somewhat shorter, he disconnected every radio that was permanently connected to the battery, and the drain was negligible. He deployed relays to activate these leads to the battery when it was started. Since this very intense modification of the radios' power connections, I had had a negligible drain on the latest installed battery in the vehicle (less than 15 milliamps) when the car was turned off. The current battery is working to its specifications, never failing to start the car. I no longer use or need the charger to sit on the battery when it's in the garage.
I also wanted to mention that I have not lost any memories in the four above-mentioned Motorola radios that were previously connected directly to the battery. All four radios work flawlessly, with no memory or settings loss.
Luckily the previous batteries were under warranty, so that was not a monetary loss to me. Because it took a week for the installer to completely re-wire all the "A-leads" from direct connection to the battery, now going through relays activating power to the radios. The relays provide +12VDC from the battery. The only things attached to ignition power are the relays in the new configuration. Of course, every radio has the proper fuses on each "A" lead and has given me maximum performance with all the radios and, of course, the operating of the car with no issues.
