Car batteries have a sad life. They’re not glamorous, nobody thinks much about them, and they get little love or attention. Batteries mostly just sit in the dark by themselves without any TLC until they get sick and die, usually on a freezing cold morning while you’re late for something.

At all points between their installation and death, however, car batteries have an enormous capacity to muck up the proper operation of almost every part of your vehicle if they’re not kept healthy. A weak or dying battery can cause electronic gremlins to take over your car, and an old and tired battery will likely just fail to start your engine one morning, sometimes with little warning.

When this happens, you might try to replace your own battery and hopefully you have some experience or can ask a skilled friend or mechanic.

Either way, just be careful or you might wind up like the victims of these two posts from the popular subreddit r/justrolledintotheshop that showcases some of the Internet’s worst car fixing fails.

In this post, u/redflamehot shows us one of the many ways not to change the battery in your vehicle. In this example, one end of a ratcheting wrench has welded itself to one of the battery terminals, and the other has melted through the battery casing.

This happened when the operator of the wrench made the mistake of contacting both battery terminals at once with a metal object. Instantly, this caused a tremendous amount of heat (and noise, sparks, and smoke), and the battery began to melt within seconds.

This treatment also introduces a risk of electrocution, fire, and explosion.

We’re not sure what happened to the operator of the wrench, but if they happened to have any popcorn kernels in their pockets, they probably had a nice snack for the post-electrocution ambulance ride.

Collateral damage, according to u/redflamehot, totalled at least $600 for wiring repairs, new battery not included, which is an additional chunk of change. That figure could quadruple if the vehicle’s ECU was damaged by the massive electrical short as well.

In modern cars, a battery replacement may require special tools or procedures to prevent damage or issues with other on-board electronics like the alarm system, immobilizer, safety systems, and driveline computer modules. A botched DIY battery change on the wrong vehicle could brick the vehicle, resulting in a pricey tow truck bill and repair/reprogramming costs.

Oh, and while we’re at it, definitely don’t install a battery that’s a bit too tall and then slam your car’s hood back down on top of it. That’s what happened in this post from r/justrolledintotheshop. In a three-second video clip, we can see a cool-looking electrified hole through the vehicle’s hood, caused by a puncture from one of the battery terminals underneath.

Although this presents another safety hazard, numerous commenters in this post wonder if this approach to battery installation creates a new type of anti-theft system, though we wouldn’t recommend it.

Lesson learned? Make sure you or whoever is replacing your battery knows what they’re doing, unless you like surprise repair bills (and possibly skin grafts).