CAUTION: For the little bit of hiking-related content it offers, this post has a lot of words ... for something hiking-related I encourage you to skip to something else!
The discharge rate of a good quality low-discharge NiMH is low enough that you do not have to worry about topping it off if it has been charged within the last year or so. You are also ignoring the fact that primary batteries also self-discharge when not in use...
After telling me that I’m raising a concern that’s minor, why are you then raising an ‘also’ that’s an order of magnitude even *more* minor?
This is correct as far as you state it, but it is only a minor issue for NiMH if you use a good charger (and is easily erased with a rejuvenate cycle or two).
Well yeah, if you call largely discharging and recharging a battery a couple of times in order to avert or alleviate memory effect ‘minor’. Batteries come with a lifetime that’s expressed as a maximum number of charging cycles. Each such act by a ‘good’ charger exacts a “ding” against that lifetime. In contrast, Li-ion’s do not require this pyrrhic form of ‘rejuvenation’.
A great application for batteries like this is indeed in something like a power-hungry GPS, where deep discharges are encountered frequently in routine operational use. I’m also very intrigued with the Prius approach which has successfully fostered 7-year plus NiMH battery life by keeping the battery perpetually near the center of its charge/discharge cycle – but I digress—I can’t really think of a hiking analog to this application, given that hikers don’t (at least yet) carry supplemental generating capacity...
You can also view lithiums as having a very severe memory problem--you use them once and they have no capacity left no matter what you do...
Since we’re already discussing lithiums as a *disposable* alternative to restoring a NiMH battery to full charge, exactly how is that observation advancing the conversation?
(BTW, do not ever try to recharge a lithium primary cell.
Um, well of course ... when did I ever suggest that people should?
NiCd's have their uses, but are a poor choice for hiking.
I agree - did I inadvertently recommend them as a good choice somewhere?
Any rechargeable battery can be topped off.
Well yes, if per the memory effect discussion above you call periodically exacting a full discharge/charge cycle on your battery over and above actual operational use ‘topping it off’. Li-ions do not require this – they can simply be topped off.
Li-ion's must be used only in equipment and chargers designed to use them--they would be destroyed very quickly if directly substituted for NiMH, alkaline, or lithium cells (even taking the voltage difference into account). The different shapes and sizes protect against substitution.
Well of course you can only use them in devices that are designed for them. FYI, 3.7V Li-ion AA’s *do* exist, and it would indeed be imprudent (unless you’re a pyromaniac) to insert one into a device that’s hoping for a 1.5V battery. I’d like to see devices whose power supplies can take advantage of any input voltage that’s present within a range (ideally 2.5V-7.5V), much as AC adapters these days commonly can accommodate input voltages of 100V-250V.
There’s an analog to this in one of my favorite movies. Remember when Christopher Lloyd flits in from the future in the DeLorean, realizes he’s low on energy, finds a discarded beer can that’s half full with who-knows-what, pours it into the car’s Mr. Fusion, and is then good to go? If and when I ever decide to deal with a GPS, I'll want it to be able to make do with whatever AA’s I have on hand in a pinch or have decided to use due to situational cost advantages.
In fact, something remotely approaching this already exists today: BD offers a headlamp model, the ReVolt, that can differentiate disposable AAA batteries from proprietary rechargeable AAA batteries, in the former case refraining from attempting to recharge them. The differentiation method is crude, but with industry cooperation could certainly be improved upon – ideally via a battery standard that’s analogous to PnP on PC’s.
Also the low temperature performance of Li-ion is similar to that of NiMH. (Only primary lithium cells are significantly better.)
My first-hand experience is that NiMH’s in cell phones 10 years back tended to quit on me mid-conversation at around 20°F. Similarly, when I would try to fire up my cold laptop in the car (being careful to avoid condensation), it wasn’t interested in playing along until 20°F+. These days, Li-ion’s (camera and phone) don’t start annoying me badly until the mid single digits. Not as good as Li disposables I agree, but hey, I’ll take it! And who knows, maybe NiMH has improved on this score since those days.
BTW, Petzl and Princeton-Tec make Li-ion powered headlamps. (I prefer headlamps with readily-available standard-size (eg AA or AAA) field-replaceable batteries.)
Moi aussi. I’m currently almost finished with a full migration to AAA - my two Spot's (BD Spot and Spot Messenger) dragged me there - but I likely still will carry an AA flashlight as a group-wise “just-in-case”.
Yes, GPSes do beep to warn one that the batteries are getting low. However in practice one often doesn't hear them. Also NiMH and lithium cells have rectangular discharge curves that give little warning that they are nearly empty.
Sounds as though it’s time to lobby for better annunciators – Let alone you, the current state of the art can unleash noises that could wake the spirits from any old Indian burial ground that you may be trampling. And the mAH’s remaining at the tail of those rectangular discharge curves would be more than enough to get your adrenal gland pumping.
BTW, while your knowledge of battery technology appears to be above average…
Wow, thanks for the compliment! To receive my patch, do I need to attend the dinner?
... you are clearly missing some of the details--you might find
http://www.batteryuniversity.com/ to be a good reference.
In today’s fast-paced technical environment, we’re all missing some of the details – the key is to be abreast of enough of them to make informed decisions where needed, and to know where to go for more if necessary. Always glad to get a recommendation for an additional quality reference for when I may need it.
(My background is that I am a PhD electrical engineer with a long interest in batteries.)
You may also have been able to detect that batteries have been on my brain for a while as well. VI here also. I notice from the alumni directory that there’s LL in your background, likely making us kindred spirits on yet another dimension.
Alex
Beyond that, I log my waypoint times by hand [
