Using rechargeable batteries in a backup light?

[fmerkel]

The link giffenk posted is pretty decent. Batteries do not have a straight line discharge curve. Most of them have some kind of an 'S' with voltage dropping quickly at the beginning, slowing down in the middle, the dropping precipitously at the end. You also don't get a very accurate indication of what the 'real' voltage is with a simple voltmeter, open circuit as he says. (Those little boxes with red/yellow/green) are semi-useful for alkaline, and mostly useless for NiXX.). You really need to put some kind of load on the battery and a lot of what you get is determined by the load you put on it. The real test is the load you put on in the field. Batteries in a low draw light will be different than a high draw light, and yet different in a strobe.

The S-curve is less pronounced for alkaline (more linear), and more pronounced for NiXX and Li-on.

Alkaline is fine for a backup light. Probably that is what most people ought to use. I just recently advised someone to do just that. But for a smaller minority that understand how these chemistries work and have the tools to deal with it we tend to use batteries appropriate to the job we have at hand.

 

[JohnnyC]

I use alkalines because I can get them anywhere in the world, they last long enough in a set of backup lights that I can rotate them to household stuff every 6 months when I swap them in my lights, and I don't have to mess with them. I don't have to buy chargers, I don't have to search high and low for decent rechargeables just to make sure I don't get screwed, and I never have any trouble traveling with them.

I have plenty of other stuff that requires my attention when cave diving, I don't need to split my time and resources more on something so simple to source as alkaline batteries.

 

[Doby45]

I have yet to find an alkaline 18650 battery anywhere. As my backup lights are two DGX600s my options for batteries are limited to 18650s. Any battery I have gets charged the night before diving. Lights, GoPro and anything else. The only alkaline battery I run is in my Petrel 2 and I carry a 4pack of those batteries in my dive bag.

 

[fmerkel]

I have yet to find an alkaline 18650 battery anywhere. As my backup lights are two DGX600s my options for batteries are limited to 18650s. Any battery I have gets charged the night before diving. Lights, GoPro and anything else. The only alkaline battery I run is in my Petrel 2 and I carry a 4pack of those batteries in my dive bag.

There's no such thing as a alkaline 18650, at least I've never heard of one. If it was alkaline it would only be 1.2v (nominal), unless someone stacked 3 in series, but then the capacity would be pathetic.

You could also use and LSD AA in your Petrel. An Eneloop would give you similar run time and be rechargeable.
A 14500 Li-on would also work although I see no great benefit over an Eneloop.At that size there is essentially no capacity advantage, only a voltage advantage which can be useful in some lights for brightness, BUT at the expense of run time.
The Shearwater site states: [Trustfire and Ultrafire can be good, but seem to come from a wider variety of sources and many users report getting duds.] I would only recommend Ultrafire to sworn enemies. Trustfire is very hit and miss so probably better avoided unless you KNOW you have a reliable source.

 

[Doby45]

There's no such thing as a alkaline 18650, at least I've never heard of one.

That was kinda my point.

 

[tarponchik]

That was kinda my point.

So this boils down to "I use rechargeable batteries because I bought a torch that uses the kind of batteries which are only available as Li rechargeables and can't be physically replaced with disposables; not because I find rechargeables more convenient than disposables." Correct?

 

[stuartv]

So this boils down to "I use rechargeable batteries because I bought a torch that uses the kind of batteries which are only available as Li rechargeables and can't be physically replaced with disposables; not because I find rechargeables more convenient than disposables." Correct?

Or is it "I find rechargeables to be more convenient, so I bought a light that uses them and it so happens that there are no compatible disposables (but I don't care)"?

 

[Doby45]

So this boils down to "I use rechargeable batteries because I bought a torch that uses the kind of batteries which are only available as Li rechargeables and can't be physically replaced with disposables; not because I find rechargeables more convenient than disposables." Correct?

That more or less boils it down with exception to the second statement. I do find rechargeable more convenient than disposables in some applications. The light I bought was because it was a highly regarded inexpensive backup light. It is also just happens to only accept 18650 batteries which are only made in rechargeable format. Win/win to me..

 

[KeithG]

So this boils down to "I use rechargeable batteries because I bought a torch that uses the kind of batteries which are only available as Li rechargeables and can't be physically replaced with disposables; not because I find rechargeables more convenient than disposables." Correct?

Not really - it boils down to: I purchased current technology that make the old rules seem stupid...

 

[KeithG]

Not really - it boils down to: I purchased current technology that make the old rules seem stupid...

Kind of like still having a predive checklist than requires you to make sure your J valve is in the proper position...