Battery Capacity...?

[JAshley73]

I was recently shopping for more Fenix 18650 batteries, as I had two go through a washing machine recently, and ruin whatever protective circuitry that Fenix installs in their batteries. (Yes, very lucky that the cells weren't exposed to water, and start a fire inside my washing machine! One was even inside a water-tight match-stick container, that came open inside the machine!)

Warning: Nerd Math Below...

Anyway, I see that they have multiple AH-capacities available, at different price points of course. I wanted to see which would be the best value, so I created a quick MS Excel file to compare cost vs. capacity. What's interesting is how much less expensive the lower capacity batteries are, and how much more cost effective they are.

But, that value closes once you add a waterproof (but not washing-machine proof) match-stick container for each battery. Image below.


Thoughts? Is it worthwhile to buy more, smaller capacity batteries, but change them out more often? Or is there that much value in carrying fewer, longer lasting batteries?

 

[Maj]

I would suggest it depends upon how long the trips you do are, how likely are you want to chang a battery halfway through a trip and is that likely to be in a dificult location ie on a pitch or in a sump. Factor in also the extra weight of carrying addition batteries if likely to drain a lower capacity battery. For cheap effective battery storage container I use a short length of 20mm plastic pipe with push fit couplings on each end. I have one that carries a single 18650 and one that carries two.

 

[skippy]

I would suggest it depends upon how long the trips you do are, how likely are you want to chang a battery halfway through a trip and is that likely to be in a dificult location ie on a pitch or in a sump. Factor in also the extra weight of carrying addition batteries if likely to drain a lower capacity battery. For cheap effective battery storage container I use a short length of 20mm plastic pipe with push fit couplings on each end. I have one that carries a single 18650 and one that carries two.

Look what I just happen to have at hand

 

[JAshley73]

I would suggest it depends upon how long the trips you do are, how likely are you want to

I forgot to factor in... If I send another one through the washing machine, I'll be out less money if I buy the smaller/cheaper ones...

The plastic tubing is clever, though I suspet it will cost me more money, and be bulkier than the match containers.

As far as changing lights in a bad spot - I wear a small AA-powered Fenix HM23 around my neck like a choker-necklace. I could lose my entire helmet, I still have a backup light on my person.

 

[PeteHall]

As far as changing lights in a bad spot - I wear a small AA-powered Fenix HM23 around my neck like a choker-necklace. I could lose my entire helmet, I still have a backup light on my person.

There are various discussions on here about backup lights, so I won't reinvent the wheel here, all I will say is that you've hit my principal requirement for a backup (you can lose your helmet and still have a light), but possibly a trick.
If you use a backup light (or two if you cave alone) that uses the same battery type as your primary light, you can interchange batteries in the event of a light failing for reasons other than a flat battery. You basically give yourself a lot more redundancy for no more kit.

 

[JAshley73]

If you use a backup light (or two if you cave alone) that uses the same battery type as your primary light, you can interchange batteries in the event of a light failing for reasons other than a flat battery. You basically give yourself a lot more redundancy for no more kit.

Eventually maybe. I outfit myself, my wife, and two kids, so the gear list adds up. Slowly though, I'll keep adding lights/batteries. I'm not sure I'll want to wear [a duplicate of] my primary light around my neck though. It would be doable, but much more noticeable. That small AA-powered light is pretty small & handy. And I just throw an AA battery inside one of the match-containers, so it doesn't add much bulk to the kit. (Although you are correct, that things aren't quite as universal...)

 

[wormster]

You won't get as many charge cycles out of the lower capacity cells, plus you also get quicker fade over time.

Best spend your bucks on decent Moli cells over cheap Sanyos!!

 

[aricooperdavis]

It's not all about capacity - you also want to look at reliability, discharge curves, temperature stability etc. Personally I'd go for some Samsung INR18650-35E's or Panasonic NCR18650B's from a reputable supplier (not Amazon).

For even more battery nerd maths, check out: https://lygte-info.dk/info/batteryIndex.html

 

[JAshley73]

I thought that Fenix added circuitry to their batteries that made them longer, thus regular 18650 cells are too short to fit correctly in the battery compartments.

Am I mistaken?

 

[aricooperdavis]

I have no idea to be honest, I don't care much for Fenix lights, but an 18650 is by definition 18mm diameter and 650mm long.

I appreciate that primary manufacturers tend to produce flat top cells which may then be enhanced with a protruding button top, but a well designed light should be agnostic (and button tops are the defacto standard in consumer electronics).

The classic hack of adding a magnet to the end may work, but will increase resistance, the chance of mixing up the polarity, and the faff factor.

If Fenix are producing a light that requires a special Fenix battery to function then I'd be buying a different light to protest against that sort of behavior.

Edit: here's their "18650". It's 3.2mm too long because they add protection on both the top and bottom for impact resistance.

 

[Fulk]

For what it's worth, I have some 'nitecore' batteries that I use in a Fenix lamp with no problems at all.

 

[JAshley73]

I have no idea to be honest, I don't care much for Fenix lights, but an 18650 is by definition 18mm diameter and 650mm long.

I appreciate that primary manufacturers tend to produce flat top cells which may then be enhanced with a protruding button top, but a well designed light should be agnostic (and button tops are the defacto standard in consumer electronics).

The classic hack of adding a magnet to the end may work, but will increase resistance, the chance of mixing up the polarity, and the faff factor.

If Fenix are producing a light that requires a special Fenix battery to function then I'd be buying a different light to protest against that sort of behavior.

Edit: here's their "18650". It's 3mm too long because they add protection on both the top and bottom for impact resistance.

They (Fenix) are easy to find/buy here in the USA, and they seem to have the best information about their products. I bought Fenix over others - Zebralight, O-Light, others - because they had the clearest information, specs, etc about their products. And they're affordable, which is nice. And they offer IP68 rated products, which I felt was pretty darn important considering our caving environments...

(To be clear, I didn't really want this to be a Fenix-brand pro/con discussion - just more general talk about battery capacities - but I'm fine with the conversation going wherever...)

I have thought about using a "spacer" to make up the difference in lengths between the Fenix, and a "standard" 18650 battery. (I'm a machinist by trade, so I could whip up whatever in that regard with ease.) It's probably not worth it in the grand scheme of things. Just one more thing to lose/fiddle-with in a harsh environment, under stress...

Thanks for the link above about battery info. I'll check it out for sure.

 

[caving_fox]

I would suggest it depends upon how long the trips you do are, how likely are you want to chang a battery halfway through a trip and is that likely to be in a dificult location ie on a pitch or in a sump. Factor in also the extra weight of carrying addition batteries if likely to drain a lower capacity battery. For cheap effective battery storage container I use a short length of 20mm plastic pipe with push fit couplings on each end. I have one that carries a single 18650 and one that carries two.

^this.
If most trips are likely to be within the capacity of the cheaper batteries, buy those. Then on odd/rare longer trips you can carry the weight and plan on changing out.
Planning on routinely having to change batteries which could be avoided by buying better ones, seems like a poor idea, and I'd go with the more expensive route. Every time you break the battery compartment seal/connections you risk problems. I wouldn't choose to do this routinely if it can be avoided.

 

[Ian Ball]

I thought that Fenix added circuitry to their batteries that made them longer, thus regular 18650 cells are too short to fit correctly in the battery compartments.

Am I mistaken?

Big battery

 

[PeteHall]

an 18650 is by definition 18mm diameter and 650mm long.

I think you mean that an 18650 battery is 18mm diameter and 65.0mm long

 

[wormster]

I think you mean that an 18650 battery is 18mm diameter and 65.0mm long

Nominally, nominally, we find vereances in the dimensions, if you measure a Sony HCM cell it's slightly under but Moli P28 it's slightly over.

As capacity increases you have to stuff more coils into the same package - leading to phatter cells!!

 

[PeteHall]

As capacity increases you have to stuff more coils into the same package - leading to phatter cells!!

Indeed, which is why you sometimes struggle to fit high capacity rechargeable batteries into some torches...
The torches being made at the lower level of acceptable tolerances and the batteries being at the upper end. It's a total pain in the arse.
I have a single AA Fenix (I forget the model number) which I bought as a backup, but cannot use, as it won't take a rechargeable and I refuse to buy a new battery for it for every trip. As I won't go underground without my backup light properly charged, the Fenix is completely useless in this application.

 

[Fulk]

Sorry Pete, but I must be missing something here.

I refuse to buy a new battery for it for every trip.

Surely you'd only need to buy a new battery if you used it . . . but as a back-up light it wouldn't get used very often?

 

[aricooperdavis]

I have a single AA Fenix (I forget the model number) which I bought as a backup, but cannot use, as it won't take a rechargeable and I refuse to buy a new battery for it for every trip. As I won't go underground without my backup light properly charged, the Fenix is completely useless in this application.

I've got the HM23 and it has a very narrow tolerance range - some rechargeable AAs fit and some don't. Energizer NH15-2300s seem to fit reliably, and their datasheet suggests they're bang on spec.

 

[JAshley73]

I have a single AA Fenix (I forget the model number) which I bought as a backup, but cannot use, as it won't take a rechargeable and I refuse to buy a new battery for it for every trip. As I won't go underground without my backup light properly charged, the Fenix is completely useless in this application.

Not sure who their UK distributor is, but I would write/call them, and ask for a replacement. Their USA distributor has been excellent. They covered (2) lights that failed at the same time, under warranty, then let me select a different/cheaper/better model, and then gave me promo-codes for the negative-balance, all without much fuss. I was very pleased by them.

I've got the HM23 and it has a very narrow tolerance range - some rechargeable AAs fit and some don't. Energizer NH15-2300s seem to fit reliably, and their datasheet suggests they're bang on spec.

I have 4** of the HM23's, and I've been rather happy with them. I use Energizer NH15-2000? I think rechargable batteries, without issue. They (supposedly) don't offer the same capacity as regular alkaline batteries, but that's no worry for me, as I just carry some backups with me in the cave & swap as need. My youngest still uses one as his "primary" light. As mentioned earlier, I wear mine as a "backup" like a necklace.





**The crummy thing about caving with a family of 4, is that it requires 4x the kit to buy. Most of the time they have an OK time though, and when only 1-2 of us caves, we have lots of "backups" to equip ourselves with. I'll also have plenty of kit too, if ever my friends & family accept a bloody invitation to try caving with us...