Compatibility and interchangeability between different cordless power tool batteries is a massive problem. Few mfgrs are compatible with each other ^, and even within one brand, often older and newer tools will use a different battery connector. ^ This is true even when the voltage of the tools is the same.
Makita, for example, has two different 12 volt systems, the older "pole" connector and the newer CXT blade connector. At least, within the CXT system, all the tools and batteries are interchangeable, and there are at least two different sizes of batteries (2.0 Ah and 4.0 Ah). They also have a very nice little unit that clips on top of a CXT battery and provides a 5 volt USB charger at 2.1A in addition to the standard line of power tools. For the 18 volt systems, or LXT, all the same items and more (even a coffee maker) are available, but they are not, of course, compatible with the 12 volt systems. Some of the larger Makita tools (chainsaw, snow blower, etc...) and a few professional series tools (circular saw, etc...) are available as 36 volt systems, which is accomplished with slots for two LXT 18 volt batteries. This is the LXT X2 system and uses the standard LXT batteries.