Electric Vehicle Discussion List - Repairing Melted Battery Terminals

WARNING: This information is for your information, education, and entertainment. Please don't think of it as instructions for doing battery repair yourself. Not to scare you, but batteries can produce stupefying amounts of power - easily up to 50kW. They contain sulfuric acid and/or other chemicals which can cause severe skin and eye injury. Many types produce and retain hydrogen, which can explode. Repairing terminals requires high temperatures and open flames. Stay safe! Leave this work for an experienced professional.

Even if they ignore the studs and use clamp-on terminals, some beginners may use cheap ones, such as the auto parts store replacements that fasten the wire with two bolts and a saddle. Poor quality terminals, loose terminals, or terminals of the wrong size can cause increased resistance in the connections. EV driving currents can easily approach or even exceed 500 amps, and these poor connections generate heat - sometimes enough to literally melt the battery post. If you're lucky, the car just stops running. If you aren't so fortunate and the cable makes random contact in the battery box when the post lets go, the fireworks can get mighty interesting!

If you've been spared the fireworks, you can probably save the battery. A good battery shop can often repair it by casting a new post onto it. (By "good battery shop" I mean an industrial battery supplier, rather than an auto parts center or a discount battery warehouse.)

These descriptions by EVDL members explain how a battery pro might go about fixing your damaged battery.

Roland Wiench: I've been doing post remolding since the 1970's. Instead of using the standard auto post molds, I use a heavy duty post mold. My molds have an enlarged base plate. All my molds are the size of the usual positive post (the larger one). [A battery shop will probably use a smaller mold for the negative post, since most people will have smaller clamps on their negative battery cables. -Ed]

I use a leading oxygen-acetylene torch with a pencil thin flame that is about 4 to 5 inches long. The standard No. 1 or 2 torch head flame is too short and will blow out when the tip gets too close to the post mold.

I use a welding work-holding tool that puts down pressure on the post mold onto the base of the battery. Otherwise, the lead could float the post mold off the battery, and run out. The holding tool has a magnetic base with a clamp to hold any tool.

After the post mold and tools are in place, I cover the top of the battery with wet towels. I then preheat the inside of the post mold and battery lead base just to the point where the lead starts to pool. Then I insert pure 100% lead wire into the flame. This builds up the new post. It's important to not stop at any time. I keep adding lead until I get to the top of the post mold, then just a little more to form a convex top.

The 100% lead wire comes in sticks for leading auto body work or metal roof work. Wire lead is also available in 1/8 to 1/4 inch diameter from fish and tackle shops.

Bob Rice: I always wear SAFETY GLASSES, or nice Harbor Fright goggles! For starters, I open the caps, and blow the hydrogen out, so I don't get a surprise when I get a torch flame around a battery. Hydrogen hangs around if you don't make an effort to get rid of it!

The "button," for lack of a better term, is that large top of the area above the post that goes through the battery's plastic case. On ALL batteries, after I hack off the battery builders' attempt to give us a terminal, I grind the top shiny with the grinder, dab with flux, and apply something to make a REAL post. I have a set of terminal casting molds, made of aluminum, that USED to fit the older batteries with larger "buttons." Gotta upgrade, then I'll be able to take ANY useless terminal on any battery, and cast up a real automotive post. The Trojan folks have used an insane bunch of useless posts on their current offerings of batteries.

Steve Clunn: Over the years I've tried lots of ways to repair melted battery posts, like making a form and pouring melted lead in. It's tricky to get the lead the right temperature. Too hot and it will melt everything. Not hot enough and it will not make a good connection. Taking it to a battery shop can be too expensive to justify when you have an old battery .

My latest fix is easy, cheap, and somewhat safer to do. Some of the smaller Hawker batteries - 1200s and 925s - have a brass automotive post that screws into the UPS style female threaded terminals on the batteries. I saved these when I recycled my old Hawker batteries. They have a small Allen bolt inside which you have to get out (a little work here). Now you have a nice brass automotive post with a flat bottom, which can easily be tinned (coated with solder).

I cut off what's left of the old, damaged battery post so I have a flat, clean surface. I file it flat if necessary, and apply soldering paste (flux). This part of the battery must be very clean and fairly flat. Next I tin the bottom of the Hawker brass automotive post, being sure to use a positive size post for the positive, and negative size for the negative.

I cover the battery top with a wet rag, except for post I'm repairing. This helps to keep the battery's plastic top from melting or catching fire. I set the brass post on top of the clean, flat, filed battery post and heat just the top of the brass post until the solder pad on the bottom melts and flows out on the flat filed battery post. This takes a little care, as when the solder melts the brass post will float and slide around battery post.

This works so well that I think it's as good as new. I never had a problem with that battery post again.

If you've never had any 1200 or 925 type Hawker batteries, you won't have any of these brass terminals on hand. You might try asking on the list if anyone has some, or see if you can buy them from Hawker.

Roland Wiench: That should work, using a brass post soldered or leaded to the existing base of a broken lead post. The only modification I would do is tap the lead base and brass post for a 5/16 inch brass threaded rod to mechanically connect the two, then use the solder-lead method.