Aside from the 540EZ, the newer Speedlite 550EX can also be used with the Compact Battery Pack E. You don't really need to use the CP-E2 version with your Speedlite 550EX unless you prefer to use AA-size lithium batteries with the battery pack, in which case the Pack E is not designed to do so. Using either version during a photo session, you will not see any difference in the performance as both are designed for the same reason - to enable faster recycling with your Speedlite 540EZ or 550EX. These three photos below of two local models were shot with the Canon EOS-1v and 550EX using the Compact battery Pack E. The older (discontinued) 430EZ Speedlite can also be used with this Compact Battery Pack E. Three successive shots of local models Bounced flash photography is probably one of the reasons to use the Compact Battery Pack E as the Speedlite uses up more battery power whenever it is being set to produce flash illumination this way. Weighing at only 155 grams, this battery pack is indeed compact and lightweight, without the photographer being bogged down by extra weight whenever it is being used. Bounced flash photography The Compact Battery Pack E is not recommended to be used with the Canon Speedlite 480EG, as this grip-type flash unit is a powerful unit that has a maximum Guide Number of 48 (ISO 100, meters) at its 35mm angle-of-view coverage. The 480EG is to be used only with the more powerful (optional) Transistor Pack E Set. Transistor Pack E Set This Transistor Pack E comes in two versions, Battery Magazine and Ni-Cd Pack. The former includes Battery Magazine TP and Connecting Cord E while the latter uses a Ni-Cd Pack TP and the same Connecting Cord E. With the Battery Pack version, the user needs to buy six units of C-size batteries to power the Transistor Pack E. With the Ni-Cd Pack Set, it uses a Ni-Cd Charger TP to recharge the Ni-Cd Pack TP in approximately 15 hours. Aside from being the optional battery pack for the Speedlite 480EG, this accessory can also be used with the Speedlites 430EZ, 540EZ and 550EX. Canon Transistor Pack E Set & Connecting Cord E How it is attached to the Speedlite 540EZ The Transistor Pack E, whether one buys it as the Battery Pack E Set or Ni-Cd Pack E Set, is supplied with a carrying case where the photographer can attach it to the belt or simply slip a strap into its two loops and carry the pack over the shoulder. << Back to Main . 1 . 2 . 3 .