Hot AAA Battery?

[Frontier]

So installing a new thermostat today. Popped two AAA batteries in as directed. Not sure if I put them in properly; usually do but, never say never. Few seconds later, funky smell hits me. One of the batteries is HOT. I pop it out and burn my finger superficially in the process. Other battery is fine. Put a new battery in the same slot after a few minutes; it's fine and dandy.

I tried to Google answers, but came up empty. If I'd put the battery in reversed, would that have been enough to cause it to go hot? The thermostat was in my hand, no wires attached, batteries where sole source of power. But it got hot in seconds. Has me a lil freaked over continuing this installation.

 

[gturner]

If it takes two AAA batteries and one was installed backwards, then the positive and negative ends were connected in parallel, instead of in series, but then in most circuits either the positive or negative ends wouldn't have actually gone anywhere - (for example, you connected both negatives to the circuit and tied the positives to each other, but not to anything else).

circuit ------- minus batter1 plus +++ plus battery 2 minus -------- circuit

In this case there shouldn't have been any current flow.

There's a chance that the circuit actually tapped off between the batteries (giving it a 1.5V and 3V source), which is occassionally done to give -1.5V, ground, and +1.5V. In that situation a reversed battery could cause some crazy problems, perhaps with an active power supply component directly shorting the reversed battery.

 

[RandyS]

What did you do with the hot battery? Obviously I can't say for sure, but just to be on the safe side, I'd toss it. And not inside either, throw it in an outside dumpster. I did the same when I discovered a hot battery in my TV remote once.

 

[StarryEyed]

It sounds like the two terminals in the battery box where the individual battery in question was installed are shorted together. An ohmmeter would confirm this. It would read zero ohms between the positive and negative terminals of the slot where the hot battery was installed. That would be the result of a faulty assembly process.

It might also be that the battery developed an internal short when installed. My guess is that is what happened since your second battery was fine.

 

[Rek]

Are you sure you put it in backwards? It just sounds like a defective battery - which does happen. If a labtop and a cellphone can have defective batteries then that sure can.

I would only worry if the whole device was giving off a great amount of heat and both/all batteries started to burn right away.

In short: I'm pretty sure you'll be fine.

 

[StarryEyed]

If it takes two AAA batteries and one was installed backwards, then the positive and negative ends were connected in parallel, instead of in series..

No, they would be in series-opposing and the net voltage would be zero. No heat. No anything.

If the battery box was designed for two batteries in parallel and one was reversed, the batteries would be in series with each other and both would be hot. I have never heard of a product designed like that though for obvious reasons: putting a battery in backward could start a fire.

 

[gturner]

Oops. You're right. For them to be paralleled the plus and minus terminals of the device would have to be the same point, which would be a dead short if the batteries were installed correctly.

 

[Jadzia]

But it got hot in seconds.

The battery must have been short circuited.

Does the battery compartment use springs on the negative terminals?

And is there a metal strip along the bottom of the battery holder running from the positive terminal?

Did the spring get pushed down so it was in contact with the strip?

 

[John Picard]

Sounds like the polarity was reversed and you crossed the streams.