I use 9P's with battery extensions to run the KL3, KL5, P60 and N4.
The 9P body comes in two different lengths. The latest and most common 9P body is longer than a few of the old round body 9P's. Most of the old round body 9P's are also long.
The advantage of the short body 9P, is that you can use two A14 battery extensions for a 4 AA battery flashlight, instead of three A19's, with the long body 9P. Two A14's are longer than three A19's, by exactly the difference between the short and long bodied 9P's lengths. Fewer extensions means less resistance. I have two of the short bodied 9P's, with the P60 and N4 lamp assemblies, running on 4 AA NiMH batteries.
I also have two long bodied 9P's with three A19 battery extensions, running KL3's, on 4 AA NiMH batteries. Occasionally, I put the KL5 on one, in place of a KL3. The KL3's and KL5's regulators, make up for the added resistance of three A19's, and run just as bright as when used with 123A lithiums.
The KL3 is designed for 6-9 volts. I have used six A19's on a long bodied 9P, for a 6 AA NiMH battery flashlight, with the KL3. It's very long though. Don't run the KL5 on 9 volts, as it is designed for 6 volts only.
oldgrandpajack
PS: You can use a sheet of paper from your printer, rolled around the AA batteries, to keep them lined up straight and rattle free.