You will get different voltage up an down its a common thing. If the bikes start ok i would not worry. When riding see if there is any change in the amp gauge plus or minus. As for the battery tender i think their not worth the money!
I live in Canada all i do is remove my battery and the old lady's too at the end of the season give them a good charge and store them where it,s warm. My battery is 7 years old and the wife's is 10 years with no problem. :small3d017:
Wow, do you like to play the lottery, too?
The overwhelming concensus on this forum is going to be that you're riding on borrowed time with batteries that old. Many times they'll give no indication they're about to give out until you attempt to start the bike. Hope you're not far from home when this happens!