Wrong. What appears to happen, is the battery loses some of it's capacitive reactance and becomes less of a filter. It is NOT always a matter of capacity or voltage that is causing the BCM / ABS to have a fit and not operate the wing properly. Load tests do not show this, it can still be your battery.

But I'd also suspect a wheel speed sensor OR one of the limit switches on the wing mechanism in the hatch lid. In rare cases, it's pitted contacts or flaky solder joints on the RCM.

LOOK, it's hard to troubleshoot YOUR car when WE are not standing there. Consider this:
WE ALL should be carrying a spare crank sensor and RCM. I carry both. Consider ordering a new RCM andputting it in. If that clears the issue, send the old one to DJ for reworking. If it does not fix it, you have your spare RCM for when the RCM fails in the rain on a highway as you coast to the side of the road. It is money well spent.

RCMs plug in without tools, ANYONE can change one with NO SKILLS and NO TOOLS. The RCM causes many issues: No start but crank, no start and no crank, P401 error, ABS failures, etc. DO NOT order a Crossfire part - order a "Mercedes 2003 SLK320 Relay Control module". I accidentally ordered a "2003 Mercedes SLK230 relay control module" and it worked as well, it is the same unit but one fuse is the wrong rating - didn't seem to matter.