12.6 volts is 100% charged on an idle, battery at rest for 24 hours or more with no parasitic loads.
12.5 is nearly full ... but in the same conditions... might be showing the first signs of age. NOTHING to worry about.
Immediately after charging ...you might see anywhere up to 13.4 V on the same batteries but this is what is called a SURFACE charge and dissipates over time. There is no problem with your batteries if they rest finally at 12.5 and 12.6V.
If they are wet cell batteries...you might consider a small investment in a turkey baster type hyrometer at the local auto parts store. Simply sucking up some fluid into the baster can tell you the exact condition of every cell in your battery whether at rest or under load. Otherwise...wait at least 24 hours after ANY in or out activity on the battery to take an electrical reading.
This might be interesting to some on surface charge. My friend on another forum decided to measure voltage drop in storage over a COLD winter. Here is the first picture after charging:
You can see 13.77 volts...a large surface charge on an OLD battery!
Three days later at rest....
12.9Volts is still a surface charge after THREE days! This battery at 100% reads 12.7ish.
So don't think you can get an accurate battery condition reading at less than 24 hours with a voltmeter...though anything less than 12.6 before 24 hours are up should indicate that there's at least some wear! A dummy load or a turkey baster is needed for a quick and accurate measurement of battery state.
Harbor Freight sells a 100amp dummy load for 20 bucks. Saves a lot of time if you have AGM's!