T60 battery question

[badtz]

Hi, though Im a recent member I've been trolling these forums for some time, but this is the first time Im somewhat stumped. My question might be answered somewhere on these forums, but I'm unsure what to search... Well here goes.

I have 2 T60's, one was incorrectly specced to me as a T60 with discrete graphics, which it was not, so I got one that had what I wanted. After getting both machines reinstalled and working happily I swapped the batteries and now have one machine that says the battery is not a lenovo battery, the other machine is fine. If I swap the batteries back, I get no message from the power manager app, so I'm trying to figure out whats going on. It seems one battery is older than the other (2007 as opposed to 2009), and is labeled IBM instead of Lenovo, so is there just different circuitry or something of the sort in newer batteries that is causing this? Its not really an issue, I was going to swap the lesser battery into 'my' machine and sell the other one with the 'good' battery, but being somewhat obsessive of little things like this Im curious to find out what the issue is.