I've done 12+ hour days of metal fab/wrench work - cut, grind, weld, drill, install, remove, modify, repeat, etc all day - with all M18 drill, hex impact, right angle grinder and sawzall, one battery on each (2.8's on the drill and hex impact, 5.0 on the grinder and 9.0 on sawzall) and one 2.8 in the charger (not even a fast charger) and never had an issue running out of battery. With a fast charger and 5.0's and 9.0's for all the tools I can't imagine practically being able to outrun that many batteries plus one on the charger.
The only time I had an issue with this was when I bought an M18 right angle hole hawg with an 18" long 1" ships auger bit drilling out tree stumps. I had 2 regular chargers, 3) 5.0's and 2) 2.8's (this was before the 9.0's were out) and I couldn't keep the batteries cool. Started with all 5 charged, ran it until it overheated, put it on the charger so it starts charging as soon as it cools down enough, grab another battery, repeat. I made it through all 5 batteries before the first one finished re-charging. I limped it along and finished a few of the other batteries off that had cooled down some, but realized that it was not the right tool for the job. I took it back and bought a corded model. No complaints about the tool, but the batteries at the time couldn't keep up. I'd bet the 9.0's would do a much better job.
Many of the kits come with rapid chargers and just make sure you have at least 1 more battery than tools and I would struggle to imagine a situation where you'll have a problem with dead batteries. The more tools you have the less likely you'll be to run them all out at the same time, so the obvious solution to this is to buy more tools
