Put a battery charger on the engine-bay attachment points then run the callibration.

 

Bought a cheap n55(crank, no start). The previous owner told me a shop diagnosed the car with Valvetronic shaft codes. [What DME Fault Codes do you have NOW using ISTA?] ... I downloaded ista to do the recalibration test. While doing the test, it stops it saying low voltage supply. [If you don't have a battery charger to attach to Jumpstart Terminals while using ISTA with engine OFF, see below.] The fuses in the top left of the engine bay are good. I see that there are like three relays in there. But I can't find a diagram of what those relays go to nor their part number so that I can just replace them. Does anybody know what those relays go to and what part# they are? [ISTA "SSP" wiring diagrams and component locations are attached, along with two pdf's that explain use of ISTA, for Diagnostics, and as "Shop Manual" (view documents).]...

Welcome to the Forum!
Questions:
1) What Fault Codes in the DME to you NOW have (ISTA Fault Memory)?
2) Do you have a Battery charger? If so, and if it can charge at 6Amp or 10Amp rate, connect that to Jumpstart Terminals, as Coop57 suggested. If NOT, here is CHEAP solution (that works ;-):

Amazon.com

3) What are Last-7 Characters of your VIN? Needed for correct wiring diagrams.

Attached are ISTA ScreenPrints showing the VVT circuit, Lines ID, fuse F04 Location, VVT Relay Location, & Location & Connector view of VVT Actuator Connector X6353. Also attached are ISTA ScreenPrints of VVT Live Data/Diagnosis Scan for VVT Target & Actual Angles, for my 3/2007 build N52K. I don't have an N55, but if you would like test suggestions using DMM, please advise.

The pdf: "ISTA as Shop Manual", attached to NEXT Post, shows HOW to view ISTA SSP wiring diagram documents. The attached wiring diagram is found using "valve gear" search term. Quickest search is filter for SSP & PIB (wiring diagram & pinout) ONLY, but default settings will eventually show what you want (plus a LOT more ;-)

With Ignition ON, Engine OFF, the Eccentric Shaft Angle should change when you press the Accelerator Pedal (reading Live Data). Can't tell from "low voltage supply" description, but that MAY mean that the voltage supply to the Actuator Motor via X6353 connector (to include two ground connections) is NOT 12V+, as opposed to battery in need of charge. DMM voltage measurement at Jumpstart Terminals would quickly indicate battery charge.
George

 

Attached is pdf: "ISTA as Shop Manual", which discusses HOW to view ISTA Documents, including SSP Wiring Diagrams, REP Repair procedures, etc.
George

 

I downloaded ista to do the recalibration test. While doing the test, it stops it saying low voltage supply.

"Low voltage supply" means the vehicle is on battery power alone or connected to an inadequate external supply, such as a typical consumer battery charger/maintainer. Valvetronic (re)calibration requires the vehicle to be connected to an external power supply, which is not the same as a battery charger. The recalibration cycle runs for something like 15-20 minutes. You need a power supply that can deliver enough current to maintain system voltage at ~13.5V+ throughout the process.

IIRC, you want something in the 40-50A range; that is generally considered sufficient for all maintenance needs of the E9X, including programming/flashing of modules if you ever go that route.