To change the battery in the master key for the 2008 Accord, can the small Phillips head screw be removed to take the head apart & get to the battery? What type of battery does it take? And would the key have to be resynchronized after battery replacement?
( My experience with the GM Passkey 3 system). If so, how is that done?

 

got this from wiki answers, hope it helps. 1. use a jeweler's screwdriver (i used a 2.4 philips, which worked for me) to loosen the screw. 2. pull apart the two key halves, (my key had a little slot on the side to make the at easier) and remove the little black capsule with the door lock. panic buttons etc form the key. (my Honda Accord 2010 key was a little difficult to open: it didin't want to separate at the rear and I was concerned about breaking the plastic - but screwed up my courage and applied force and it eventurlly popped open, and I could then see that my concern was unfounded) 3. You'll need to open the capsule from one end with a jeweler's (flat head this time) screw driver (note the orientation of the two halves, they only fit correctly one way - so that the contacts touch the battery negative surface and the positive landing pad) on my 2008 accord key, the battery inside was a Panasonic cr1616 3V watch type battery. 2010 accord likewise. Honda doesn't bother to include this information in the owners documentation. 5. The reason that I was opening my 2010 Accord key was weak signal and the local honda service manager told me that this complaint wa due to dielectric grease at the contact points. Sure enough, there were drops of grease on the batery negative surface and on the positive copper landing pad. I wiped the contact surfaces clean removing the offending grease.

 

Thanks for the info!

 

I finally got around to doing this. The worst part of it was loosening the small screws that hold the key heads together. They were not only overtightened, but also seemed to be glued in.
Once the key head is apart, the little container that holds the battery & buttons comes right out & can be opened by prying up on the catches at either end with a very small flat blade screwdriver. The battery can be R&Red at that point. Put it in positive side down.
Then press the container back together. Put it into the key head. Put the key head cover back on. And use as little force as possible when tightening the screw.