I learned about disconnecting the negative terminal many years ago. I was young and new everything. Had to replace the radiator in my 1990 Toyota pickup. I was not doing anything to the electrical so there was no reason to worry about the battery, right? Well, I was using a ratchet to unbolt the radiator and it slipped out of my hand. The socket was still attached to the bolt and the handle rotated around and fell on the battery terminal. A few sparks and then smoke started bellowing up from the engine bay. I grabbed a piece of wood to knock the ratchet of the battery. In the end, I ended up melting the wiring from the battery to the starter and all the wiring to the alternator. Cannot remember if I fried the battery, starter, alternator, but I thought I had destroyed my truck.

I was fortunate that nothing blew up or caught fire. That was enough for this know-it-all to never work on my vehicles without disconnecting the negative battery cable. I have gone to the extent of just removing it from the truck when I am working around that area to avoid any possible problems.

 

Bump. People still need this information.

 

Good info fmc400 and good bump black and blue. A local haul pack mechanic died a few years ago when the wrench he dropped landed on the starter connections just right and started the engine. Now even if I’m just changing oil I disconnect the battery leads in the proper sequence.

 

If you have a stiff battery cable that wants to flop back into position and contact the terminal, slip an old leather work glove over the end of the cable to act as an insulator. The glove also will cover the negative battery terminal and prevent a dropped wrench from touching both terminals.

 

I stuck a hair pin in a wall outlet once, I probably peed my diaper.


I've welded steel with a battery, jumper cables, and coat hanger.

 

A neighbor once had a battery blow - should have been an inconsequential spark but he caught fumes... sounded like a 12 gauge. Luckily he was wearing glasses, but he had an acid burn over pretty much his whole face and was very unhappy. Did not do the battery any good, either.

 

An automotive start battery is nothing to mess around with, there's a lot of potential energy contained inside.

Another angle to beware of - a 100% fully charged battery will not freeze, at least not at any sane temperature. Maybe safe to 40 or 50 degrees below zero.

But a discharged, dead, or even a 50% depleted battery now has some varying percentage of plain water, depending on the state of charge instead of electrolyte, and it will freeze solid in subzero or extreme cold.

Never attempt to jump start or charge a frozen battery. I don't have direct experience with this, but my understanding is that this is a factor in battery explosions. Exposed plates - low electrolyte may be one, and/or physical damage of the plates, separators, straps, etc. with sparks or arcing internally = Fireworks. Maybe this happens weeks or months later? I dunno.

This is one reason too why jump starting a stranger in a parking lot on those antarctic days is kind of sketchy. How do you know the history behind that particular battery, is it frozen, or waiting to go off? Rare, maybe, though it does happen. And it seems to me even if a frozen battery were completely thawed out it is probably now junk anyway, only good for a core and not worth the risk.

Keep your schitt on a Tender, reason #4,352

 

I am learning things about batteries to this day. Gota love good ol FTE!

 

I always remember it it "Black off first, Black on last". Simple and easy to remember.