My Spectra has arrive. It has a 6.2v 4SR44 battery wich is PX28 equivalent. The meter's manual says that use a 6v PX28, so the battery aparently is not the correct. I used it a little bit taking readings. Do you think I can damage the meter using a 6,2v battery instead a 6v?
There also are modern, lithium based replacements called a PX28L that deliver true 6V - these are far more constant than alkalines, but still have a considerable voltage drop towards the end of their life. You can safely try using PX28L, they will do no damage. Just bear in mind that a unstabilized meter using a PX28L will be off (compared to silver oxides) by a constant value (usually less than one stop, but you'll have to figure that out while you still have something to compare to!) for about half the battery capacity (i.e. weeks or months of use), and will get increasingly unreliable (alkaline like) after that point.
On the positive side, lithium cells have a shelf life of five to ten years and generally will not leak even when dead - wherever the cameras/meters can deal with them, I do prefer them to the rather leaky silver oxide and alkaline cells for that reason.