Over the years, many Mk4/Mk4.5 Focus ST owners have experienced recurring battery-related issues, ranging from inconsistent Stop/Start operation to low voltage warnings and module errors. Rather than having information scattered across multiple threads, I’ve pulled together input from owners, forum discussions, specialist advice, and real-world testing into one structured guide.

This document covers State of Charge behaviour, Stop/Start logic, battery replacement options (EFB vs AGM), correct BMS reset procedures, safe charging methods, and commonly used ForScan adjustments. The aim is to provide a practical, evidence-based reference that reflects what has consistently worked across the community.

It is not official Ford guidance, and any changes are carried out at your own risk, but it should give owners a clear, consolidated starting point for diagnosing and improving battery performance.

FOC Battery Diag and ForScan Guide March26 V.1.pdf

Good idea! I had long been considering doing something similar myself – no need now 🤣

It might be worth contacting the FOC moderators to see if this could go into the Ford Focus Guides section. I would imagine, like many things it could continually evolve, expand & improve as more owner info becomes available, and experiences shared. Assuming that this is largely targeted at FOC members, it might help to cross-reference some relevant posts/threads from the Focus forums. As you indicate, there's a lot of valuable discussion buried away in these forums.

I appreciate that you would want to maintain ownership/credit but personally, I found the current, heavy font, watermark across all pages is distracting from the main content. You might consider, a lighter font, or perhaps add your name as an every page footnote.

In any event, well done for starting this useful guide!