Hom many tenders on one circuit?

[mncruiser]

We added 2 more bikes to the family this season so along with the tractor, we will have 5 batteries to tend. Last year we had 3 to deal with and I had them all sitting on the bench in the basement and all on the same circuit via a surge protector power strip. My small work room only has one plug in it so my question is, how many battery tenders can/should you have on one circuit? Is it a bad thing to have the batteries/tenders all next to each other?