I apologize for any confusion, you are correct that there is a difference in mass between a fully charged and uncharged battery, however the difference is so small that it is not measurable using current technology. The difference in mass is on the order of micrograms or less, and would be extremely difficult to detect. To calculate the difference in mass, you would need to know the energy stored in the battery when fully charged and when empty, and use the formula E=mc^2, where E is energy, m is mass and c is the speed of light. However, it's important to note that the difference in weight would be so small that it would not have any practical impact on the usage of the battery or your e-bike.