Not accurate at alll. but it gives you rough idea about your battery condition. My ciggie lighter voltmeter readings were 12.8v, when plug in charger to charge phone it drop till 11.5v, sometimes drop till 10.Xv then i know its time to add battery. and at least you know your alternator is working.

My obd2 reader, 13.1v to 13.5v all the time. so plug the voltmeter direct to battery is still the best option.

that car just 2 years + old oh.

Agree it is not the product that is not accurate and i never blame the product oh, but it is the way it is connected that make the readings inaccurate. there is too many things before it reaches the ciggie port, then ciggie port got more resistance. then ur handphone charger, gps, ionizer , shaver, all dragging power, lowering the voltage in that ciggie port(this i dont understand why only the ciggie port voltage drop till 10v and others still maintain 13v).

thats why i suggest that connect voltmeter direct to battery is still the best option.

But ciggie lighter voltmeter is still useful for rough idea of the battery condition. I myself is still using ciggie lighter voltmeter because i don't want to temper my wiring and lazy to open up my hood to check the battery voltage.

okie, will check see any problem or not. thanks.

but usually when drop till 10v. it is time to add battery water. after add then it goes back to 11v when i charge HP.