Review on Multifunctional Car Charger with 3 USB Ports, Voltage Meter and Socket Splitter - Compatible with iPhone, iPad, Apple Watch, AirPods, Samsung, LG, HTC, GPS, Android Phones - Black by Bill Forbis

Most digital voltmeters are accurate to within 1%. I don't drive much and when I plugged it into my cigarette lighter it showed me 12.1 volts, for a lead acid battery 12 volts flat, 12.5 volts fully charged. So I hooked up my little 6 amp charger to charge the battery. The voltage slowly increases, with a small 6 amp charger my charger can read 13.5 volts in the morning. About half a day after I unplug it, or when I use some power, it will probably go back to 12.5 volts. A larger charger can reach 15V while charging. (I've been working with batteries for about 10 years.) Holds up well to an outlet. I always connect a GPS to my cigarette lighter for the speedometer and to know when I hit 322 miles when my tank is empty after filling up. Sometimes I need a small USB port to charge my tablet, it has three USB ports. I'm fine, I'm happy, that's what I needed.