I agree that my suggestion adds more than a little record keeping. It also requires the GM to spend some devoted time to assigning values to powered items. I tossed and turned all night, the idea grumbling about in my head. And I hadn't even given any thought to Craftsmanship. But if a GM, any GM, wants to add a sense of "don't fail me now" to the scenario it's going to require extra effort on the part of the Players and the GM. It would be effort well worth the time spent.
All Power Checks use one d10.
Rather than basing an item's energy reserve on it's general design and function, requiring the GM to assign individual values to every powered item, perhaps Craftsmanship could be the basis for assigning values.
Poor = 6+
Common = 5+
Good = 4+
Best = 3+
Then, depending on the level of tension the GM wants to set for an encounter or investigative scene, taking into consideration the function and purpose of the device(s) being used, the situation and the experience of the Acolyte(s), he/she could assign modifiers, much the same way as he/she would assign Difficulty Levels for Tests.
(Using the Difficulty descriptions already provided in the Core Rules for ease of translation)
Very Hard: -3
This modifier could then be further adjusted if a PC has the Tech-Use Skill (or similar): Failed Tests would not affect the operation/use of the device unless failed by more than 3 DoF, and then only resulting in a -1 Power Check penalty modifier. Each DoS adds +1 bonus to the "Power Check" (?) roll, up to a maximum bonus of +3. In these instances, such Tech-Use Test could be considered Free Actions, based upon the PC's familiarity with his/her own gear.
No Power Check score may be worse than 10+ or better than 2+. After all, there has to remain some level of stress, even if it is quite small.
Rather than concerning oneself with the need to recharge items, it can be assumed that all but the most specialized gear (such as Portable Cogitators) have a self-regenerating energy cell. If the encounter or investigative scene is meant to be nothing "special" then items can simply function as they were designed to do so, as needed. Power Checks may subtly increase in Difficulty once the GM decides to ramp up the suspense and tension. A Tech-Priest with Luminen Charge might be considered as constantly mindful of his/her gear's readiness, providing a +2 bonus modifier to any and all Power Checks made by the Tech-Priest. Technical Knock could be used to prepare the Machine Spirits of items, awakening them for operation, providing a +1 Power Check bonus modifier; with the use of this Talent the Tech-Priest may awaken the Machine Spirits of gear owned by others, preparing a number of items equal to his Intelligence Bonus per day, each item requiring the very minimum of a Full Action. At the GM's discretion, an additional bonus modifier of +1 might be gained if the Tech-Priest offers proper observances to the Machine Spirits, requiring approximately ten minutes per item and the application of Sacred Oils/Unguents/Incenses. Preparations last no longer than one day; Machine Spirits don't like to be taken for granted.
Example: Orpheo and his companions are skulking through the undercroft of an abandoned church. The church sits far out in the wilderness of the moors, a region of unnatural chill, dense fogs, and ill reputation. The unnatural chill has seeped into the undercroft, wracking Orpheo and his companions with juddering shivers, even through their protective clothing. Orpheo hears a low growl, but before he can call out a warning to his companions he is toppled over by the lunging hulk of the dreaded Moorhound. In a desparate gambit to drive the creature off himself, Orpheo thumbs the power stud on the grip of his trusty Chainsword and takes a hurried swipe at the creature's snarling muzzle.
"Trusty" Chainsword (Good Quality Craftsmanship) = 4+
Unnatural chill/ill reputation of the moors: -2 Power check modifier
The situation is grim, but not unexpected: Ordinary (+1) Difficulty modifier
Orpheo's Tech-Use Skill (Trained, 33): Test result of 12, 2 DoS (a Free Action, therefor unable to alert his companions to the sudden attack)
The Power Check on Orpheo's trusty Chainsword is now a 3+; he rolls a 5, and with his Chainblade chiming around its well-oiled gears, its motor revved to a keening pitch, Orpheo catches the Moorhound a glancing blow along its flanks. It is not enough to seriously injure the beast, but Orpheo has driven it from atop himself, and now stands, his stance wide and balanced, the throaty purr of his Chainsword vibrating the close air of the undercroft as the beast menacingly prowls back and forth within the dark shadows, nothing visible of it except for its gleaming red eyes…
As a final note: Just because an item "fails" doesn't mean it's useless. Subsequent Power Checks (which really are outside of the normal structred time and therefor are a game mechanic requiring no time…other than for the beneficial uses of Tech-Use/Luminen Charge/Technical Knock) would grant a cumulative +1 bonus modifier each Round, to a maximum of +3, so that eventually a panicking PC has finally shaken and cursed his gear to life, and thus possibly aiding the preservation of his/her own hide.
This method is simple compared to my previous suggestion, not unduly compliated, but still something toward added tension or suspense.