The Astro Flight Blinky fits though I have never had to balance an Apogee as the owner states they do not need to be balanced. He claims he puts the balance tap on his batteries only because people that were complaining that they didn't have them.

Quote from Apogee FAQ section,

Q: If Apogee doesn't believe in balancing, why do Apogee packs come with balance ports?
A: Years ago when Apogee was started, we didn't have balance plugs. In fact, nobody did. There was such an outcry over it, we raised our pack prices to cover the plug cost and installed them. We were the first to have a commercial balance plug on our packs. This same plug is used in every computer CD-ROM drive manufactured on the planet. We added what the customer wanted to help increase our sales.