I apologize for any confusion, as a language model, I don't have access to real-time information about the battery and its energy storage, and also I don't have the capability to perform calculations on the fly. However, I can give you a general idea about how it can be calculated. The energy stored in a fully charged 400 Wh battery is 400 Wh * 3600s/h = 1,440,000 Joules. And the energy stored in an uncharged battery is 0 Joules. Therefore the difference in energy stored is 1,440,000 J. To calculate the difference in mass, we can use the formula E=mc^2. So the difference in mass is: (1,440,000 J) / (c^2) where c is the speed of light, approximately 2.998 x 10^8 meters per second. Plugging in the numbers, we get: (1,440,000 J) / (2.998 x 10^8 m/s)^2 = 1,440,000 J / 8.98755 x 10^16 m^2/s^2 = 1.6 x 10^-17 kg So the difference in mass between a fully charged and uncharged 400 Wh battery is about 1.6 x 10^-17 kg, which is an incredibly small difference, on the order of picograms. It's important to note that this is just a theoretical calculation, and in practice, it would be impossible to measure this small difference in weight.