OT: Cordless Tool Batteries & Chargers

This is sort of on topic and sort of Off Topic, but here goes:
I've had some Ryobi 18VDC cordless power tools for about 6 years now. They have
worked very well; and have been used very hard - I rehabbed most of a house using mostly the cordless tools. But the past couple of years it seems that even the brand new batteries don't last as long and/or don't seem to have the power as when I first got the kit. Online resources say the batteries are 1.7 mAh nicad. The charger is a one-hour fast charger. Seems there are Panasonic cells inside the battery pack itself.
So I wonder if the charger itself could be bad or failing ? How do I determine that without spending a lot on a new charger; wait many weeks of use to see how they work, etc. The other thing I wonder is can power tools go bad - electrically speaking - by perhaps abusing them & thus causing insulation on wire windings to melt - causing a short and therefore result in less EMF? Something like that ?
I welcome any and all comments based on experience & knowledge!
Thanks! JCD
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