How to tell a dead battery from a good one

[zinger1457]

OK battery experts, what causes a battery to leak and what if anything can one do to avoid it? One night last week my DirecTV remote control was working fine one minute then all of a sudden it stopped. When I went to check/replace the batteries only one came out, the second battery was stuck. Had to completely disassemble the remote control to get to the battery which wasn't as straight forward as one would think. Sure enough the battery (Duracell alkaline) was all corroded at the end and had expanded enough that it wasn't easily coming out. I've had batteries leak in flashlights that hadn't been used in a long time but this is the first time I can recall this happening with an item that I use daily.

 

[NW-Bound]

What, a ton of gearheads on this forum, and they let the above question go unanswered. I guess I will have to take this on.

The question should be rephrased "What have they done to keep batteries from leaking, as most of them don't?"

As a kid, I took apart zinc-carbon batteries all the time to get the hard graphite rod (positive terminal), and the zinc shell or body of the battery (negative terminal). The graphite rod made good electrodes for conducting electrolysis experiments, or generating sparks by arcing. The zinc when dropped in sulfuric acid from weak discarded car batteries reacted strongly and released wonderful bubbles of hydrogen, which burned with a nearly invisible flame, very hot and caused nasty burns. But I digressed...

So, the way the old zinc-carbon battery is constructed, the caustic pasty electrolyte eventually eats away the zinc shell, and leaks. This being an acidic solution has a nasty habit of eating away the metal parts of the appliance, or the terminals of the battery housing. Very, very bad and aggravating.

Alkaline batteries have an alkaline electrolyte (duh!), and when leaked do not cause the same corrosion. The mess can usually be cleaned up with a toothbrush and water, and everything is good as new.

Both types leak a lot less often now. I don't know how they do it.

About your remote control running fine on a terribly bad battery, I can explain that. Remote controls are designed to run on extremely low power, on the level of clocks or watches. It's so that they need no on-off switch. The only time they use significant power is when you press a button and they need to blink their infrared emitter to transmit a code. This however consists of very short pulses. Such bursts of electrical power can come from a small electrolytic capacitor that is built-in and wired in parallel with the battery bank. The capacitor is like a buffer that gets charged by the weak battery, and can provide the intermittent power requirement that the infrared emitter needs.

So, that's how a remote control can still operate off a practically dead battery. It's like catching drips from a leaky faucet with a glass, so that you can still quench your thirst once or twice a day.

 

[ERD50]

What, a ton of gearheads on this forum, and they let the above question go unanswered. ....

I was waiting for the chemical engineers, this is a chemistry problem!

Related to that, I recall a very bright engineer I worked with. He wasn't an EE, he was a physics major. He said it made no difference, it's all the same stuff, he just had to learn the electronic specifics. But he was a very bright guy, so easy for him to cross disciplines.

He also made the claim that there was no such thing as an electrical failure. The electrons always did exactly as they were expected to. Electronics failed due to mechanical problems (broken wires), chemical problems (like those batteries, or dendrite growth on circuit boards), or later, with embedded software, due to programming problems.

Back to the question though - I think this is related to the other thread on the bounce test for a dead battery. As the chemicals change form, they expand, leading to leakage.

Lithium keeps getting better and cheaper, maybe alkalines will be out of circulation someday soon - though they need to improve the self-discharge rate of lithium before that will happen.

Reminds me of another story. When my son was a teen, he went to buy batteries for his portable CD player, and figured 'Heavy Duty' batteries must be really good. I had to explain that term came about in the 40's or there-a-bouts - yes, they were better than the old carbon-zinc, but awful compared to modern alkaline. They must be a few cents cheaper though (or less likely to leak today?), because if electronics come with batteries installed (like in a remote), they are usually the old type, not alkaline. Save a few cents on a $1,000 TV?

-ERD50

 

[ls99]

THe physics guy is correct. Electrons will always do the expected.

When still in the Light rail business one fellow ignored procedures and ended up contacting 750 Volts DC. For practical purposes unlimites current, the breakers were set for 7000 Amps, automatically re-closed three times before locking out. Damn near killed him. Months for receovery.