I tried doing this with bathroom scales.
I jacked the car up and put three wheels on blocks so it would be level, then the 4th wheel sat on a large plank with the 4 bathroom scales underneath.
It would have worked had the bathroom scales played nice but they were digital and didn't like staying on for more than a few seconds.
I got numbers but wouldn't guarantee how accurate they were.
Using a public weigh bridge was probably more accurate.
Front axle only Full car with me and some extra bits in so remove 100kg
The dry weight is around 1550kg so with a full tank of fuel and all fluids probably close to 1650kg.
I guess that means I've added approx 200kg with the conversion but I have 38kWh battery that's good for 100 miles range.