VEX Battery accident


Recently, we had a incident with a vex 7.2 battery that powers the remote.
The incident is as follows
Unplugged battery from charge station
Turned on vex robot
Connected battery to the controller
-Everything is fine until the battery in the controller is connected.-
Battery starts smoking. I immediately unplugged the battery from the controller and as soon as it was removed it began glowing red hot on the internal contacts.
Placed it in the sink, and put it out with water ( I know your not supposed to put out electrical fires with water but I had to stop the smoke to prevent the alarms from triggering ) as of now it is leaking battery acid in the sink. It has cooled off and has a cup over top of it to prevent a fire.

First question is, why did this happen? It wasn’t a error on my part, at least I don’t think so.
Secondly, how do I dispose of this battery, and make sure it doses catch on fire?
Please help.

Please reach out to the VEX tech support group so they can work with you to get to the bottom of this.

[email protected]

They’ll help “make this right” immediately.


I’d like to see some pictures if you can post them.

It sounds like you had an internal battery short. This can be caused by a piece of metal getting inside and causing the cells to conduct from one to another. The FTC battery cells are metal all around and conductive. If the insulation around them is worn away, it can short to the robot frame. One of the FTC teams I’ve worked with had a battery short to the frame of the robot and the there was a return path back to the battery which provided a short circuit. The path bypassed the battery fuse and the mishap caused a motor controller to catch fire.

For disposal, dispose of it as you would any NiMH battery (I think that’s the correct type). Your local area should have some way of disposing of old batteries.

Here are the photos, sorry for the bad quality but that’s the best I could do

Photo 2 of the bottom.

What model camera are you using?

I am using my iPad camera.

Using water is the correct method of extinguishing a Li-Ion pack. But is not for electronics because it will likely short out more things.

This is a NiMH battery pack, it shouldn’t catch fire spontaneously again after the damage it has sustained.

Top end = connector end
Bottom end = end opposite connector

Well, the batteries went into thermal runaway. Cause TBD. Unfortunately this is one of the failure modes shared with Lithium Batteries (see 787 for more details). The cells at the bottom appear to have swelled and cracked. The cells on top look to have burst and were probably the source of the smoke.

Does the controller still work?
What happened to the insulation & wire on the cells at the bottom of the battery?
Was it dropped recently?
Any idea how old the battery is?

At this point, the cause seems most likely due to a cell to cell short internal to the battery pack. This would lead to thermal runaway in the cells causing the deformation and smoking. Placing it in the pack was probably the straw that broke the camels back in the internal insulation.

At this point, the battery has been disposed of. As far as i could determine, the battery was intact, not new, but it had not been used too much. I will test the controller on monday, and figure out if it had anything to do with it. Before
The incident it showed no signs of damage except for a scratch here and there on the plastic insulation. It may have been dropped,but if it was, it wasnt by me. As of after the incident, much of the insulation had burned away around the tops and bottoms of the cells inside. all wires were in good condition. Until the cause is determined we have locked up all the batteries of this exact kind. As for its age, we bought them last year.

To be clear, the battery that did this is not the battery that powers the vex microcontroller, rather the one that powers the handheld radio controller.

That is, of course, only if you care about the electronics more than you care about extinguishing a fire.

A small low-voltage battery is best extinguished in water, because of the large cooling capacity of the water. The goal is to get it to cool off.

Electrical systems that use voltages high enough to cause a shock must not be extinguished with water, as the water stream is conductive and can cause the person directing the water stream to get a lethal shock.

That being said, the BEST time to fight a fire is the moment it starts, when it is smallest. Just a warning though: If you are fighting a fire and it is getting larger, run away, warn others, and run away more.

To add on to this:

New electronics can always be bought. Your safety cannot.

I’d much rather replace all of our electronics and hardware than have someone get seriously injured from a fire.

Like Don said, if the fire isn’t going out very quickly, you should run away very quickly!

To clarify what I meant by short out, I DO NOT mean it will further damage your electronics(which it will do). I mean it will short out more AREAS causing an increased chance for additional areas to overheat and catch fire unless you are SERIOUSLY hosing it down while it sputters to a stop.

The 787 plane, not the team :wink:

If you can keep the iPad close for long enough it will focus in a macro mode (I know and share your pet peeve, Ether!). The iPad unfortunately doesn’t have a flash, so the exposure will still suffer under those fluorescent lights.

We do still have the battery lying around, i might be able to get some better pictures tomorrow, I was in a rush. If I do ill post them here