The Logis Implant requires a Toughness test or you take a level of fatigue. The other Tech priest talents with similar drawbacks (e.g. Luminen Blast) can be offset with the Energy Cache talent. Does this talent also work with Logis Implant?

Personally i'd say yup.

It's just another bit of augmetic gear the Techpriests have ways of using better than other people as they have the "body of the omnissiah" to deal with it.

No. Energy Cache specifically gives a finite list of three talents in works with. Logis implant is not one of them.

RAW aside, I'd still say no. I read the fatigue caused by Logis Implant to represent mental rather than physical exhaustion, so a better flow of power wouldn't help with that.

Radomo said:

As the above poster said. If you look on p.115 of the DH Core Rulebook, you'll see that the Energy Cache can only be used when "...using Luminen Charge, Luminem Shock and Luminem Blast." The v.3 errata doesn't alter this either - only the fact that you roll against your Toughness, after use, to see if the level of fatigue is gained i.e. the fatigue gained is not automatic.