In Australia, I only buy genuine DeWalt batteries when special discounted offers with tools if possible. Haven't tried aftermarket, too hard to decided good and bad as all look 'real.'
If you are using different brands of cordless, many slip on adapters available to ie run Makita on DeWalt batteries. So you can run everything on one battery type. Converted a B&D pole trimmer, (14.4 volt) to DeWalt 18 v battery and runs well.
Dewalt are supposed to be stopping manufacture 18v (as marketed in Australia) / 20v range this year or next, to concentrate of 54v (marketed in Australia) / 60 volt flexi volt, but too late for me to start again and no longer working as much. But maybe the state of the economy might postpone this?
No doubt batteries will be available for many years to come, can only suggest try one recommended, if good buy more ASAP before different batch/ manufacturer.
I only use 4 or 5 Amp/ hr batteries, and used on angle grinders/ drills/ saws/ blowers/ and line trimmer, (which is underpowered compared to fuel options, but serves a purpose.) Portable fan is only 2 amp hr battery I have , and lasts well, or just use 5 amp hr.
PS. Although DeWalt promote use of the flexi 60v battery in 20v tools for better performance/ longer usage, a few on the internet point out magic smoke experiences. Never tried myself.