Noticed the other day that my voltmeter on my Passport 8500 showed 13v while driving down the interstate going 70MPH. I thought maybe something was wrong with the radar detector so I plugged it into a friends car and it showed 13.8v at idle even with his system turned up. Back into my max for a couple days just to look at stuff and noticed this morning with lights and wipers and defrost on it was at around 12.4v with my system off. Any ideas? The battery is an optoma red top that was bought a year ago.

 

Measure the running voltage at the battery with a good volt/ohmmeter. Don't rely on that radar detector to give accurate data.

 

Like old said I wouldn't trust a radar detector. Measure the battery when the car is off. Then turn on the car and measure it. It will be about 14v while running cause the alternator should be charging it. If not, I know a site which will show you how to replace it. Its a pain in the *** but saves you some cash. Took me about two hours. I replaced mine yesterday.