My battery charger says 15.2
But my multimeter says 15.8 ?
Both are cheap products, charger is 3-4s hot RC
What one should i go by ?
Thanks in advance guys.

You need to have a reference voltage. You can buy something like the link below to calibrate your equipment. Otherwise, your guess is as good as mine.

KKMOON High Precision Voltage Reference Module AD584kH 4-Channel 2.5V/7.5V/5V/10V https://www.amazon.com/dp/B00Z033Y6Y/ref...ACbCN03P77

If you have a diode you can check the voltage drop across it with your multimeter. It should read 0.7v. Maybe check some known voltage sources like a usb ps or pc ps rails. I have some cheap lipo voltage testers, even those don't differ 0.6v from my multimeter .

Get one of the devices that Voodoo linked to. If you're working with precision electronics you should have one in your toolbox. Pictures of mine in use are below. They're inexpensive so it's worth just getting one.

The 4 reference voltage outputs have been measured with a high end precision meter (in the case below an Agilent/Keysight 34401A) in a controlled temperature condition (21 degrees Celcius), and on the back the person at the factory who tested the device writes down the actual voltage you should see on the screen of your DMM for each of the 4 voltages. In the case below, the 5V output of the voltage reference device should actually show 5.00132V on a DMM. In the case below my DMM goes to 3 decimal places so it is rounding the value to 5.001 which confirms that my DMM is perfectly calibrated and will show true 5.000V if the source is outputting a true 5.000V.

If you find the calibration is off, then inside the meter there are usually some calibration trimming pots you can adjust to get the meter to show the correct voltage.

   

I want to share photo too. Nice DMM you have there. I also have a cheap Craftman which I calibrated. And the Craftman is dead accurate.

(17-Feb-2019, 02:32 AM)voodoo614 Wrote: I want to share photo too.

Snap!  

We used Flukes during my apprenticeship days and I always promised myself I would get one. I got fed up of using crappy cheap meters, so about 4 years so I finally decided to pull the trigger. I did grimace a bit at the cost but I have no regrets. These are the gold standard of DMMs IMO and are "Made in the USA" so you know you're getting a top grade product that has been properly quality tested  You don't generally need to worry about calibration with decent quality DMMs because they've been properly calibrated at the factory and they rarely seem to go out of calibration. Mine is still in calibration with no re-adjustment having been made even after 4 years of use.

Apologies to the OP for going slightly off topic, but hopefully you get the idea about how to test the calibration of your equipment, or be able to adjust the calibration so it is giving a reading that you can confidently rely on.

Thanks very much guys , i will look into everything you all have suggested.
Big big help .
Thank you .