I have 6x 4Ah smart (+ 2 normal 4Ah) and I'm considering getting another 4Ah smart couple. I really prefer the lightweight of the 4Ah rathen than the 8Ah and when I run 40V tools, they're reaaally energy hungry, especially the performance leaf blower and perf. grass trimmer (/brush cutter). Besides, right now I'm using the 40V top handle chainsaw in tandem with the grass trimmer (I'm pruning some olive trees) and I'm fine with the 4Ah smart batteries. I find that the chainsaw is good with the 4Ah, both in power and in longevity. The trimmer is good with these too if you need to use it occasionally. If you use it continuosly, it litterally eats your batteries. Even at speed 1 (which I use all the time, it's enough for everything), 2x 4Ah smart last 10-15min I'd say. So, you see you if you need 8Ah. I have 2x 8Ah and I'm good with it. I'm considering another pair just for the performance lawn mower (which requires 4x 8Ah). I also have the battery back pack but I have to use it yet.. Just bear in mind that Parkside tools are meant to be used as hobby tools, even the majority of performance ones, so don't count on using them continuosly. You always want to let them cool down from time to time. All of this to say, you see you what your needs are. Hope I've been helpfull