Using rechargeable batteries in a backup light?

[stuartv]

I saw a mention in a GUE thread about not using rechargeable batteries in your backup light.

I searched for threads on this subject and only found one, which was several years old, and in the DIR subforum where I did not have privileges to reply.

The argument I read against using rechargeables in a backup light seemed to be this:

They self-discharge much quicker than alkalines.

This concern seemed to be couched in a context of having a backup light that you never use, and you replace the batteries in it every 6 months to a year. Or, you test them with a voltmeter and replace them if the voltage has dropped below some threshold (ostensibly, the voltage printed on the battery - e.g. 1.5V). Or, if you actually end up using the backup light, then you replace the batteries before your next dive.

Is that really the only argument against using rechargeables in a backup light? What other concerns are there?


All my lights are handhelds that take either 18650 or 26650 rechargeables.

I have a charger/tester. I test my batteries periodically to confirm their capacity. All my 18650s test over 3000mAh and all my 26650s test over 5000mAh. At least, all the ones I use. I have others that test lower because they are low quality. Mostly, they are the batteries that came with some of the lights. And one set of batteries I got on eBay (and subsequently got a refund on).

I never leave any batteries in my lights over night. If they went in a light, I put them in the charger that night. If they've been sitting for more than a couple of weeks, then I charge them all again before I leave to go diving.

I feel much more confident with this process than I would feel with carrying a backup light that had been sitting with alkaline batteries in it for 5 months unused. But, I realize that could be unfounded confidence.

Is there something about my process that makes it less safe or reliable than using a backup light with alkalines (even for deep-ish deco dives)?

I read one comment about the risk of opening and closing the light more often, versus opening it once every 6 months to change batteries. I feel like the flip side of that is I inspect my O-rings more often and grease them as necessary.

NOTE: I understand that a backup light needs to have enough burn time to get you from the furthest point in your dive back to the surface, with adequate safety margin. Call it double. My comments and questions are based on a presumption that the backup lights in question do have adequate burn time to meet these requirements with their rechargeable batteries. I know my lights all have WAY more than double the burn time that would be required to get out from the longest/deepest dives I have done or will do any time soon.

 

[PfcAJ]

Imo the process you describe is sound but it has a lot more potential for goofin' up over "throw them in the trash every 6 months and buy new ones".

 

[fmerkel]

Ever heard of [alka-leaks]? I've had more devices ruined by leaking alkaline batteries...
I don't much trust them at all.

I think that old men's tale was back when people used old style NiCad or NiMh. They had a pretty nasty self discharge characteristic. Couple that with low capacity and you had a problem.
With the new LSD type NiMh that is no longer a problem. Yes, you can get them in C and D size if you really want.

A 'consideration' could loosely be called performance/internal resistance. Alkaline batteries need to 'make' the current which is not an aggressive chemical reaction. They are limited in the current they will support.
The higher the performance (ability to put out current) of a battery the lower it's internal resistance generally is.
So....if a low resistance battery floods in saltwater it will short and potentially dump a lot of current fairly quickly. This can have various consequences, none of them good. OTOH, there's nothing good about flooding an alkaline device either.

FWIW I use old style quality Sanyo NiCads in my 3 C-cell UK SL3 backup. I've learned that I really ought to open it up a few times a year, check and grease the O-rings, and make sure nothing bad has happened. I've had 2 of them 'weep' (couple drops/dive) which adds up to damage over time. (UK replaced them).

I see no particular issue in using NiMh LSD, 18650, 26650 in backup devices, this is assuming they are decent batteries and not Ultrafire or other junk.
I've had quality re-chargeable cells go 10 years with regular use.

 

[KevinNM]

I've been told that people have found that leaving a rechargeable battery in a car in sunlight, where it hits like 160, can have pretty bad effects on the charge in that battery. Which you will discover when you need that light.

The usual reason why GUE has these policies is that something very bad happened or came very close to happening to someone.

 

[tursiops]

Policies based on the quality of a technology need to be updated as the technology improves.

 

[KevinNM]

Policies based on the quality of a technology need to be updated as the technology improves.

There might be few like that out there... But it is what is is for now.

 

[fmerkel]

I've been told that people have found that leaving a rechargeable battery in a car in sunlight, where it hits like 160, can have pretty bad effects on the charge in that battery. Which you will discover when you need that light.

The usual reason why GUE has these policies is that something very bad happened or came very close to happening to someone.

Which would possibly make an alkaline leak like a sieve.
High temperatures are bad for ALL batteries, all of them. At 160*F chemistry is somewhat irrelevant.
Are the GUE police going to open your devices and check your batteries?
A LOT of the new lights won't even take an alkaline cell and they are being adopted by the tech community like crazy. They are simply way better.

If GUE made a rule every time something bad happened they couldn't even get in the water anymore.

 

[tursiops]

There might be few like that out there... But it is what is is for now.

NiCads, then NiMH, then Li, then low discharge Eneloops......it goes on. Policies based on NiCads are out of date big time. The mistake in the policy was in calling them rechargeables. Now all the new rechargeables are also damned.

 

[stuartv]

Are the GUE police going to open your devices and check your batteries?

I don't care about that. I just care if their policy is based on something that makes my process less safe than their recommendation. From what I'm gathering, it is not (as I am not using NiCads).

@fmerkel's point seems particularly relevant as I could see a backup with alkalines being left in a vehicle for prolonged periods during that 6 months between replacements where my batteries for my backup lights would never sit anywhere (except their bin in my house) for very long between the time the battery was charged and the time I use it. Maybe a couple of days, at most.

 

[Bob DBF]

Considering what your personal policies are, I have no problem using them in a backup light. Rechargeables are much better than they were, and if you keep track of where your batteries are, and how well they keep their charge, I don't see a problem. I watch my rechargeable batteries and move them from critical uses to non-critical uses, as the batteries loose their charge more quickly, and dispose of them on a regular basis.

On the other hand, if you are not meticulous and doing advanced dives, then you have bigger problem than your backup light.



Bob