Cave Diving Backup Lights / Rechargeable Batteries

[Superlyte27]

I just did my CCR cave course. I did notice when I was reading the Tao of Cave Diving it still says to use non-rechargeable batteries in your backup lights.

I think if you compare the lights used today as backup lights, many of them have a similar burn time to the primary lights from days gone by. I’d be comfortable with rechargeable batteries in at least one backup light if not both.

nm, I googled it.

 

[tursiops]

NiCd batteries suck. They were the standard rechargeable when the dictum arose to not use rechargeables. And, as with so many things, rules never evolve, even if they should. Actually, it is still a perfectly good rule if you replace the word rechargeable with NiCd; back then, the words were equivalent, today they are not.

 

[Capt Jim Wyatt]

NiCd batteries need to be discharged fully before recharging else they get a "memory" based on the amount of discharge prior to their next charge -- i.e. if 50% discharged prior to charging and recharged after this cycle of usage becomes routine you lose 50% of the capacity of that battery.

 

[kensuf]

Jim, you probably also used to use a wet cell nicad primary light that you could hot charge off a car battery in the parking lot between dives. One of my mentors was still using that technology in the mid-90s (YIKES!) and he was also overdriving a 6v bulb to 7.2v. It was bright, when it didn't blow up... I was blessed to start this sport at a time when lead acid "gel cell" batteries were in use for our primary lights, they were heavy, but inexpensive to replace and were good enough for a 3 hour dive if you had brand new batteries and took care of them.

I'm in the "still use disposable batteries in my backup lights" camp. I know that the majority of people are now using 18650s, and those are definitely more reliable than the NiCAD batteries that had memory problems and quick discharge rates back when I started cave diving. However, any rechargeable battery is only as good as it's current charge.

My rules on backup light batteries:

1. I replace the batteries on my drive home anytime I've used a backup light on a dive.
2. I replace the batteries every six months regardless of whether or not I use them. My personal schedule is 4th of July and Christmas.

To those that never heard of these concepts, be thankful that battery technology has evolved dramatically and you're able to reap the rewards of these advancements.

 

[Capt Jim Wyatt]

Jim, you probably also used to use a wet cell nicad primary light that you could hot charge off a car battery in the parking lot between dives.

Yes that was what my first cave diving primary light was. Built by Frank Martz. Whopping 45 minutes of burn time driving a 100 watt aircraft landing light. The electrolyte was a 5% solution of Potassium Hydroxide which had to be topped off regularly because charging off the car battery/alternator boiled the contents of the cells vigorously.

We have come a LONG way since those days.

 

[macado]

When I did my cave training in 2012 my instructor was also adamant that backup lights use Alkaline / non-rechargeable batteries. I believe this is an outdated approach now, hear me out..

I carry 3 backup lights on every cave dive or 2 backup lights and a 3rd extra handheld primary light in my pocket for longer / bigger dives. Is it excessive? Maybe? They're small and unobtrusive. Stuffing a third light in my pocket does not really take up too much real estate. I'd hate to be the one to call a dive ~100ft into a cave if my primary fails. I know we've all been there but if I have a suitable primary handheld light in my pocket the dive can be "saved." I am not breaking any rules since I still have 2 working (verified) backup lights at my disposal.

But to answer your question about today's usage of backup lights. The technology has evolved where I feel lithium battery lights are safe for backups provided they have the necessary runtime for the dive planned in question.

• Lithium is a much more stable battery chemistry than NiCd and NiMH. Slow discharge rate with Li-Ion cells. Good-quality 18650 cells (not Chinese ones) have decent capacity (E.G., Panasonic, LG, Samsung)
• Today's LED backup lights are much more reliable than old halogen bulbs. No bulbs to break or burn out. They can be dropped and abused. Yes I know LEDs can burn out and drivers can fail but overall I find LED light more reliable.
• Today's LED backup lights are a magnitude brighter than most old school canister Halogen lights or backup lights. I've literally been on dives where a team member had a primary light failure, they called/aborted the dive and the third team member did not realize why we turned until we were out of the cave. (One could argue poor buddy awareness but I am just making a point that most backup LED lights are pretty bright).
• Today's primary lights are far more reliable than old school canister lights. Less fragile. Even newer HIDs are less fragile. My Light Monkey 35W HID light is 9 years old. It's on the original bulb and ballast. I have two of them. The only thing I've had to do is replace the cable but the bulb / ballast is original.
  
  
  EDIT: The one thing I forgot to mention. 18650 cells should still be topped off and re-charged, checked periodically. I also burntest my backup lights in a bucket of water.

 

[RTodd]

Alkaline batteries can but put on a volt meter and you know whether they are still good. LiIon are way better then the prior alternatives but you still can’t use the voltage to gauge burn time as definitively as with alkaline. Fully onboard with carrying a second Li Ion primary but don’t understand any push back on the simplicity of having two alkaline backups.

 

[Lorenzoid]

Alkaline batteries can but put on a volt meter and you know whether they are still good. LiIon are way better then the prior alternatives but you still can’t use the voltage to gauge burn time as definitively as with alkaline. Fully onboard with carrying a second Li Ion primary but don’t understand any push back on the simplicity of having two alkaline backups.

The way someone recently explained to me their rationale for sticking with alkaline-powered backup lights was that they discharge more linearly, getting progressively dimmer before going dark entirely. It seems to me this rationale might have carried more weight when batteries had shorter burn time. Maybe the thinking back then was that on a longer dive you might have to judge when to switch to your second backup light.

 

[rddvet]

Been cave diving since 2013 and was taught then to use nonrechargeable batteries in backups. The tech on rechargeables is tremendously better, but I still won't use them. For me it's about ease. I put a note in my phone to check them every 6 months (or just replace them). I also replace them anytime I plan to travel out of the country to dive (since I'm already pulling batteries out for the airline anyway). If they ever get used, the battery is changed afterwards. That is probably excessive, and to be honest it feels very wasteful and not eco-friendly. But I try and be as eco-friendly as I can be in other places.

 

[rjack321]

The way someone recently explained to me their rationale for sticking with alkaline-powered backup lights was that they discharge more linearly, getting progressively dimmer before going dark entirely. It seems to me this rationale might have carried more weight when batteries had shorter burn time. Maybe the thinking back then was that on a longer dive you might have to judge when to switch to your second backup light.

yes but the energy density is terrible compared to li-ion
and you can't have too many lumens or the burntime will be minimal
so you end up with a lower powered light that doesnt last as long as something using a better battery
when you are scootering out on a backup racking up crazy deco at depth, having a high powered light and doing a full speed+ exit is potentially life saving