You can find the answer to your question in the support ticket you have submitted about the same topic.
I am posting the answer here in case someone else is interested in the topic:
Thank you for contacting us. We try to keep our API similar to the API of MS DataGridView to allow easy migration. However, sometimes we change the interface to make it easier. You can do the same with RadGridView with the following code:
Find more about RadGridView in our online documentation and check the examples in our demo application. If you need further assistance, we will be glad to help.
VoltageGrid.Rows(2).Cells(5).Value = VoltageGrid.Rows(1).Cells(4).Value
All the best,
the Telerik team