Broken battery terminal repair/work around?

[LittleSister]

I've broken the positive terminal of a very expensive Red Flash AGM battery (tiny size, high CCA) I had yet to install (while 'borrowing' it to start another boat's engine). The terminal is M6, and I'm left with a short stub with a damaged thread.

Any suggestions how this could be repaired or worked around?

I am guessing that welding or similar could not be done without potential damage to the battery or the person doing it.
Is there any kind of conductive adhesive I could use to fix some type of supplementary terminal to the remains of the original?

I could perhaps secure some kind of bar across the top of that end of the battery using a strap under the battery, then that bar either bearing directly on a ring wire terminal on the battery's terminal base, or with a bolt through the bar to clamp the wire terminal against the remaining base, but would welcome suggestions of other potential solutions.

(First 2 photos show the undamaged negative terminal. The last photo shows an M6 nut just nipped on the top of the damaged terminal thread, which allows me to clip my battery charger to it for the moment, but doesn't give enough contact area or pressure for a proper secure connection for engine starting amperage.)

 

[Davy_S]

Photos not showing. They are now but i cant find out how to delete, sorry.

 

[Rum Run]

Hmm, interesting.
Your clamp idea would be a runner - maybe using a piece of Tufnol as the cross bar.
I think it would be possible to very carefully TIG weld a chamfered piece of M6 studding (or cut-off bolt/screw) onto the stub, taking a while to cool down between intermittent bursts of current. Needs an experienced operator though - not me!

 

[Rum Run]

Photos not showing.

I can see them fine

 

[Alex_Blackwood]

I've broken the positive terminal of a very expensive Red Flash AGM battery (tiny size, high CCA) I had yet to install (while 'borrowing' it to start another boat's engine). The terminal is M6, and I'm left with a short stub with a damaged thread.

Any suggestions how this could be repaired or worked around?

I am guessing that welding or similar could not be done without potential damage to the battery or the person doing it.
Is there any kind of conductive adhesive I could use to fix some type of supplementary terminal to the remains of the original?

I could perhaps secure some kind of bar across the top of that end of the battery using a strap under the battery, then that bar either bearing directly on a ring wire terminal on the battery's terminal base, or with a bolt through the bar to clamp the wire terminal against the remaining base, but would welcome suggestions of other potential solutions.

(First 2 photos show the undamaged negative terminal. The last photo shows an M6 nut just nipped on the top of the damaged terminal thread, which allows me to clip my battery charger to it for the moment, but doesn't give enough contact area or pressure for a proper secure connection for engine starting amperage.)

View attachment 196180View attachment 196184

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Can you drill and tap, insert a stud and perhaps a lock nut? Probably wouldn't hurt to go to M5.

 

[Davy_S]

I can see them fine

Yes so can i, but i could not find out how to delete my reply.

 

[Tranona]

Can you wind the nut right down and then screw a piece of studding into the top of the nut?

 

[Rum Run]

Can you drill and tap, insert a stud and perhaps a lock nut? Probably wouldn't hurt to go to M5.

Core diameter for M6 is 5mm, so maybe M4 would work, but very dependant on accuracy on axis. But how deep to go is the question - too deep opens a can of worms chemicals

 

[LittleSister]

Can you drill and tap, insert a stud and perhaps a lock nut? Probably wouldn't hurt to go to M5.

I like what the result of that would be if it worked, but I don't know what is underneath - how deep / wide the underside of the terminal is, or how it attaches to anything else. I fear I could end up disconnecting the terminal.

p.s. beaten to it by Rum Run

 

[Alex_Blackwood]

I like what the result of that would be if it worked, but I don't know what is underneath - how deep / wide the underside of the terminal is, or how it attaches to anything else. I fear I could end up disconnecting the terminal.

p.s. beaten to it by Rum Run

Or use one of these.
https://uk.rs-online.com/web/p/stan...us7-j4VOxoAsNWGXWY0aAoXjEALw_wcB&gclsrc=aw.ds

 

[LittleSister]

Can you wind the nut right down and then screw a piece of studding into the top of the nut?

The nut won't run any further down, it is only hanging on by a fragment of one turn of thread. The thread doesn't go to the bottom of the post (I now see having inspected it closely with a powerful magnifier), there's perhaps 1.5mm of unthreaded post at the bottom before the thread starts, and it's broken off where the thread starts.

 

[LittleSister]

Or use one of these.
https://uk.rs-online.com/web/p/stan...us7-j4VOxoAsNWGXWY0aAoXjEALw_wcB&gclsrc=aw.ds

That would have been just the ticket if I had any thread to screw onto!

 

[AntarcticPilot]

I wouldn't rely on there being anything much to fasten to within the case, so whatever you use has to rely only on the material you can see. I'd be trying to get a nut on the remaining thread and then screwing a stud into the top of the nut. Not ideal, but there aren't usually strong mechanical forces on battery terminals. You might need to use washers to ensure that there's enough depth of thread for the stud to be secure.

Just seen the above posts. Can you tap the unthreaded part of the post?

 

[LittleSister]

I wouldn't rely on there being anything much to fasten to within the case, so whatever you use has to rely only on the material you can see. I'd be trying to get a nut on the remaining thread and then screwing a stud into the top of the nut. Not ideal, but there aren't usually strong mechanical forces on battery terminals. You might need to use washers to ensure that there's enough depth of thread for the stud to be secure.

Just seen the above posts. Can you tap the unthreaded part of the post?

Thanks, but there is effectively no thread to screw the nut onto. There is a fraction of one turn of thread, below which is unthreaded.

 

[RunAgroundHard]

If it is a stud screwed into lead / alloy, then pour molten lead over it to form a new post, then use a clamp on battery terminal. Lots of you tube videos showing how to to do this.

For example, one of many YouTube clips showing the method, although this is a crappy repair, others show better repairs and the whole process, like scooping off the crud in the molten lead or moulding alloy before pouring.

 

[LittleSister]

If it is a stud screwed into lead / alloy, then pour molten lead over it to form a new post, then use a clamp on battery terminal. Lots of you tube videos showing how to to do this.

For example, one of many YouTube clips showing the method, although this is a crappy repair, others show better repairs and the whole process, like scooping off the crud in the molten lead or moulding alloy before pouring.

No, the terminal is in one piece (or was before it broke!) and is not lead - appears to be bright steel. I doubt lead would adhere well to it, and there's negligible upstand to support sideways loads.

 

[fredrussell]

…I could perhaps secure some kind of bar across the top of that end of the battery using a strap under the battery, then that bar either bearing directly on a ring wire terminal on the battery's terminal base, or with a bolt through the bar to clamp the wire terminal against the remaining base…

I’d go with this myself. A 1” ratchet strap wound up bar tight pulling down a ring terminal-ended piece of 35mm2 cable. No need for the bar I would have thought.

 

[Alex_Blackwood]

Probably best to buy a new battery if none of the above are suitable.

 

[shanemax]

Lead melts at about 300c, not very high, about the same temp as avocado cooking oil so make yourself a new post and use standard car battery clamps. There should be enough bolt left to make a firm connection.

 

[rotrax]

Core diameter for M6 is 5mm, so maybe M4 would work, but very dependant on accuracy on axis. But how deep to go is the question - too deep opens a can of worms chemicals

I strongly suspect the internal post is larger than 6mm. The threaded stud has been formed/cut from the piece above the top of the battery. I am VERY familiar with high output motorcycle batteries with small terminal posts, most of these have a see through clear case. The internal posts can be clearly seen. It should accept a 5mm drill and a 6mm tap.

Tranona's answer is good. Obtain an overlength nut-found easily enough online-and that should make a very satisfactory repair.