There's truth to 'dead battery bounce' after all (2015) | Hacker News Reader

There's truth to 'dead battery bounce' after all (2015)

theconversation.com

32 pointsdcminter17 comments

I have switched to using NiMH rechargeables almost exclusively now, even for low power devices (e.g. remote controls, clocks). The problem I have encountered with alkaline batteries is that they leak chemicals which can destroy the electrical contacts and sometimes the entire device. I've never had a NiMH rechargeable battery leak in the roughly 15-20 years that I've used them. But I have seen so many alkaline batteries leak that I don't trust them anymore. Maybe it's my imagination but alkaline batteries seem to leak far more often today than 10-20 years ago. Is it just me, or are Duracell brand batteries worse than others in terms of leaking?

The traditional argument for not using rechargeables on low-power devices is that the self-discharge rate for the rechargeable battery is higher than the power consumption of the device itself. However, some NiMH batteries (e.g Eneloop, https://eneloop101.com/) seem to use a special chemistry that results in only a 30% discharge after 10 years. I use the Eneloop brand pretty much exclusively. I think the extra cost of the rechargeable batteries have more than paid for themselves by avoid the damage caused by leaking alkaline batteries. The cost of NiMH batteries are now low enough that they may be far cheaper than alkaline batteries for almost all applications.

The difficulty that I have with NiMh batteries is that it is very difficult to tell when they are done charging, and they are less tolerant of overcharging and "trickle charging" than the NiCad chemistries which preceded them.

Most chargers will just assume that you've discharged them fully between uses, and perform a "full" charge cycle when one is plugged in, maybe with a temperature sensor to stop if they get too hot. You can't really use resting voltage as a gauge, and it's tricky to find a good charger which can reliably detect the small and brief "dip" in voltage which occurs around the time that the batteries are fully charged.

They're great batteries, and I also prefer them for applications where the batteries get fully drained before being plugged in, but they can still be iffy for applications where you only discharge them briefly and want to keep them "topped up".

For those applications, these days you can buy 1.5V lithium cells in AA/AAA form factors with built-in microUSB charging ports. But those are lithium-based, so you have to be careful about thermal runaway.

Life is a balancing act full of compromises...

NiCad is the devil though but I assume you didn't advocate them, just missed a property of them.

Right, good point, at least NiMh batteries aren't full of cadmium.

And has no memory which is a huge advantage.

NiCd memory effect is way overblown. It requires nearly identical cycles each time and has only ever been observed in high-capacity aerospace cells.

[edit]

Repeated overcharging can cause changing voltage curves that are (apparently) also referred to as memory effect, but NiMH cells are also prone to this.

The NiMH chargers that I've seen have a negative delta-V detection and a timer shutoff. I've had problems charging the Eneloops when used on devices that drain the battery too much. When they are inserted into the charger, the voltage seems to rise too quickly and and somehow confuses the charger so that it stops charging early. In those situations, I've resorted to charging those batteries twice. First time, charge for 5-10 minutes to raise their voltage. Then remove and reinsert the batteries to charge a second time using a more normal voltage curve. Maybe it's a quirk of my charger.

I didn't know about lithium AA/AAA rechargeable batteries. Interesting. I see that most are rated at 1200-1500mAh (AA) and 400-500mAh (AAA). These are only a little over 1/2 the capacity of the NiMH that I normally use. I guess the charging circuitry takes up room in the battery.

Got any charger recommendations? :)

And yeah, the lithium AA/AAAs were news to me too. I learned about them when I got a headlamp that could either take 3 AAA batteries or a same-sized lithium battery with +/- contacts in the right places. I think the single-cell ones include a buck converter along with the charging circuit, which probably cuts down on the space they can devote to the battery itself.

Yup, it's old but I use this Titanium Smart Fast 8 Bay AA/AAA charger (https://www.amazon.com/gp/product/B0035HCTLS). The manual states that it has negative delta-V and timer shutoff. One of the Amazon reviewers mentions a problem with deeply discharged batteries, similar to what I've seen where I need to charge the battery twice.

By the way, this situation happens mostly on my motion-activated staircase LED lights which take 4 x AA. That thing is amazing because it works until 3 x AA are essentially dead and only 1 x AA is giving out power. For most of my other devices, the device stops working before the battery voltage becomes that low.

Wow! I was asked by a friend if dead/flat batteries were weighing less, since I was working a little bit with batteries. Back then I dismissed it as utter nonsense. But I still googled the question because you never know right? and I stumbled upon either this article or a similar one: https://www.quora.com/Is-a-charged-battery-heavier-than-a-de...

After finding and reading an answer that agreed with my initial assessment I never continued to investigate why my friend would make such a claim, but now I guess it was related to this phenomenon. Guess I owe somebody an apology. Crazy how somethings seem so outlandish that I did not even ask myself if this was possible or what fundamental differences there are between batteries of different states of charge. Also it would have been quite easy to test this in retrospective... Note to myself: I should be more careful and curious in the future!

Energy equals mass times the speed of light squared.

That alone tells me a dead battery of one composition will weigh some fraction less than a fully-charged one of the same composition, assuming all other things are truly equal (number of atoms in the containing can, etc.) The fractional difference might be very, very small (billionths of a gram difference?) but should still be present.

A colleague at work tested two batteries by bouncing them in front of me. Had he merely told me about the bounce effect I would have been extremely skeptical, so I'm glad he didn't give me the opportunity to get egg on my face!

I found and submitted this article when looking for the physical basis of the effect afterwards.

I guess I was one of that day's lucky 10,000! https://xkcd.com/1053/

The linked video is something else.

https://youtu.be/ZywsCbWEun8

Now they just need to study the drop's impact on battery lifetime.

I've been using this trick to tell dead from fresh alkalines for years! I thought the science was well understood

Blast from the past, I remember doing that when I was little. Forgot all about it. Thank god for rechargeables.

Ignobel material

Reply on news.ycombinator.com