Stripped Neg (-) Battery Terminal Screw - SmartSolar 150/45 MPPT - how to salvage my mistake?

So I've done something monumentally stupid and I'm hoping someone here can talk me down before I do anything worse.

Been wiring up the solar array on my static caravan — 4 x 200W panels feeding into a Victron SmartSolar 150/45 — and in a moment of absolute brain fog I overtightened the negative battery terminal screw. Felt it go soft under the screwdriver and my stomach dropped. Classic stripped thread. The screw turns but bites on nothing.

The controller itself powers up fine off the PV input and the Bluetooth is visible in VictronConnect, so the internals seem okay. The damage is purely mechanical — the threaded insert in the housing has had it.

Few questions:

1. Is the threaded insert a standard M6 or M8? Wondering if I can carefully drill it out and fit a helicoil insert. Done this on aluminium housings before with decent results but never on power electronics.

2. Has anyone sent a 150/45 to Victron UK (via their authorised service network) for this kind of mechanical repair? I know it won't be warranty but I'd rather pay a repair fee than bin a £350+ controller. Victron's build quality is generally excellent so it seems wasteful.

3. Would a large-gauge ring terminal with a proper M6 bolt through a drilled-and-retapped hole work as a temporary fix while I source a repair, assuming I torque it sensibly and use threadlock?

Setup is 24V LiFePO4 (Fogstar Drift 200Ah), so current through that terminal isn't trivial.

Any machinists or sparks who've been here before — genuinely appreciate the input.

@WhatsAFuse65 Oh mate, I've been exactly here — swearing at a Victron controller on a narrowboat while moored miles from anywhere useful.

First things first: don't overtighten trying to "rescue" it — that just makes the crater deeper.

What you want is a screw extractor kit — Toolstation sell them for a few quid. Drill a tiny pilot hole into the stripped head, wind the extractor in, and it bites as you turn it out.

Once you've got the damaged screw free, the thread in the terminal block itself is almost certainly fine. Replace with the correct M4 or M5 stainless bolt — measure before you go to the hardware shop.

If the terminal block thread is gone too, Victron's UK support are actually decent and spare parts exist. Document everything with photos now while it's fresh.

@WhatsAFuse65 What size screw is it? The SmartSolar 150/45 battery terminals use M6 bolts if I recall correctly — worth double-checking your manual before ordering anything.

If the thread in the unit itself is stripped rather than just the bolt head, a Heli-Coil insert might save you. Had a similar panic on my shepherd's hut build last year, though I'd managed to cross-thread rather than strip completely.

One question — how badly stripped are we talking? Sometimes a slightly chewed thread will still torque up enough with a new bolt and a smear of threadlocker. Have you actually tried a fresh M6 and a ratchet to see if it bites at all?

Don't bin the unit yet is my main advice. What did you use to overtighten it — a regular screwdriver or an impact driver?

@WhatsAFuse65 Before you reach for a helicoil or start panic-ordering parts, worth checking whether the thread is actually stripped or just the soft aluminium busbar has deformed slightly around it. M6 into those Victron terminals can sometimes feel stripped when it's just compacted debris or a slightly cross-threaded start.

Clean the thread with an M6 tap if you have one — even a hardware shop tap-and-die set from Screwfix will do it. If the thread genuinely is gone, a helicoil M6 insert is the proper fix and they're widely available. Torque spec on those battery terminals is 2.5 Nm — people consistently overtighten them thinking tighter = safer, which is exactly how this happens.

Whatever you do, don't bodge it with a larger bolt. Current capacity matters at that connection point.

@CornishBoater is right on the M6.

Few things worth trying before you go nuclear on it:

• Thread chaser first — might just be mangled not fully gone
• If it's properly stripped, a M6 stainless bolt with a nyloc nut clamped from behind works fine as a bodge
• Worst case, Victron warranty is actually decent — log it on the VRM portal and contact your supplier

Had similar grief with a Fogstar battery terminal last winter. Ended up just running a new bolt through rather than faff with helicoils on thin ali chassis.

What torque were you using? Those terminals aren't meant for much — 2.5Nm iirc. Easy to go ham without thinking.

@ZFS_OffGrid and @CornishBoater have covered the thread chasing nicely, so I'll add one thing nobody's mentioned yet — thread repair inserts (Helicoil or the cheaper Wurth equivalent) are genuinely the gold standard fix here if the chaser doesn't sort it. M6 insert in stripped aluminium is a 20-minute job with the right drill and tap, and you end up with a stronger connection than the original.

One critical point though: do this with the battery disconnected completely, obviously, but also double-check your MPPT firmware hasn't logged any fault codes from whatever arcing/heat may have occurred during the stripping incident. VictronConnect will show you immediately.

I bodged a similar terminal on my cabin setup last winter — the insert saved me ordering a whole new unit. Don't panic, it's very recoverable. 🔧