Just thought I'd post this............. I now run a 14.8v pack (4 x 18650 cells in series) which gives me a 7 hour run time. My previous version used loose cells in a holder but I wasn't happy with that. I made up a battery lead that connects directly to the battery compartment contacts with small brass "screw terminal" connectors soldered with 22AWG wire. A bit fiddly to hook up (long and narrow screw driver needed to tighten the two terminal screws) but very secure and + - leads well