Using rechargeable batteries in a backup light?

[KevinNM]

I've read a lot of you postings on LED's, lights and batteries. I'd say you have a better grasp of this technology than the GUE administration probably does.

They run Halcyon. They also do 28,000 foot penetration dives. They probably have some familiarity with batteries and lights.

 

[tarponchik]

The Manual I got with my AA's (Panasonic Eneloop Pro, Ni-MH) specifically forbids to use these rechargeables in tightly sealed environment like flashlights used in scuba diving. I use them nevertheless, although in my strobe, not in flashlights.

 

[fmerkel]

Long term life is a really slippery target.
How long does a car last? >>>> Depends on the make, how well you take care of it, and to some lesser extent plain old luck.

The problem with a lot of PACKS (as opposed to single cells), is they are protected by a circuit that protects the DEVICE and the PACK.
Individual cells may.....or may NOT, be individually charged and the pack 'balanced'.
If the pack is NOT BALANCED, there will always be a couple of weaker cells. As the pack goes through cycles the weak cells get farther and farther from the strong cells. After awhile the [protection circuit] is pretty much dealing with the limitations of the weak cells. Thus, the pack becomes lame and the consumer pissed off. A new pack is then required.

If you open up that pack, and have the tools to analyze the individual cells you'll find the laggards, toss them, and may find the rest to be OK. I've got a bunch of laptop and tool pulls like that.

If your charger isn't smart enough to not overcharge a Li-on you desperately need a new charger. Whether a device has a protection circuit in the driver is very specific to THAT device and up to the consumer to determine.

 

[KeithG]

The Manual I got with my AA's (Panasonic Eneloop Pro, Ni-MH) specifically forbids to use these rechargeables in tightly sealed environment like flashlights used in scuba diving. I use them nevertheless, although in my strobe, not in flashlights.

It helps to understand why, then you can make your own judgement call:

http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

a) The nickel-metal hydride battery is designed so the oxygen recombination cycle described earlier is capable of recombining gases formed during overcharge under normal operating conditions, thus maintaining pressure equilibrium within the battery. However, in cases of extended overcharge or incompatible battery/charger combinations for the operating environment, it is possible that oxygen, and hydrogen, will be generated faster than it can be recombined. In such cases the safety vent will open to reduce the pressure and prevent battery rupture. The vent reseals once the pressure is relieved. The expulsion of gas thru the resealable vent can carry electrolyte, which may form crystals or rust once outside the can.

b) To prevent the potential for irreversible harm to the battery caused by battery reversal in discharge, removal of
the load from the battery prior to total discharge is highly recommended. The typical voltage profile for a
battery carried through a total discharge involves a dual plateau voltage profile as indicated in (Fig. 11). The
voltage plateaus are caused by the discharge of first the positive electrode and then the residual capacity in the
negative. At the point both electrodes are reversed, substantial hydrogen gas evolution occurs, which may
result in battery venting as well as irreversible damage.

So if you do not over charge them or over discharge them you will be fine.

 

[fmerkel]

It helps to understand why, then you can make your own judgement call:
So if you do not over charge them or over discharge them you will be fine.

Which is generally true for all rechargeable batteries. UK used to specifically forbid the use of NiMh in their lights, plus they had H2 absorption pellets to deal with the problem if it cropped up. I used them for years. I even did experiments where I vacuum sealed a dive light in a ziploc without the seals, and let a pack run until dead in a tub of water. I found no evidence of gas produced at all. I did that several times.

Now, once my wife forgot to turn her light (UK 400R - 18W with 4 NiMh D-cells) off after a dive. Sometime after getting back on the boat there was a loud pop and her light head flew across the boat. This was not a flood/leak/short problem. In fact the light and the batteries were all OK and continued to function normally after being checked out. I would have thought the light heads threads would have stripped, but they didn't.

Note - IMO the stobe is simply a nasty/mean light as far as batteries are concerned.

 

[tarponchik]

It helps to understand why, then you can make your own judgement call:

http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

a) The nickel-metal hydride battery is designed so the oxygen recombination cycle described earlier is capable of recombining gases formed during overcharge under normal operating conditions, thus maintaining pressure equilibrium within the battery. However, in cases of extended overcharge or incompatible battery/charger combinations for the operating environment, it is possible that oxygen, and hydrogen, will be generated faster than it can be recombined. In such cases the safety vent will open to reduce the pressure and prevent battery rupture. The vent reseals once the pressure is relieved. The expulsion of gas thru the resealable vent can carry electrolyte, which may form crystals or rust once outside the can.

b) To prevent the potential for irreversible harm to the battery caused by battery reversal in discharge, removal of
the load from the battery prior to total discharge is highly recommended. The typical voltage profile for a
battery carried through a total discharge involves a dual plateau voltage profile as indicated in (Fig. 11). The
voltage plateaus are caused by the discharge of first the positive electrode and then the residual capacity in the
negative. At the point both electrodes are reversed, substantial hydrogen gas evolution occurs, which may
result in battery venting as well as irreversible damage.

So if you do not over charge them or over discharge them you will be fine.

Thanks! I do not overdischarge cause I recharge after every 1 or 2 dives. The Panasonic charger shuts off automatically so there is no overcharge either.

Economically, the strobe is the only device where rechargeables pay off; with the introduction of LEDs, the flashlights do not eat too many alkaline batteries anymore. For example, I did 6 night dives during the last Bonaire trip and replaced batteries only once.

@fmerkel "there was a loud pop and her light head flew across the boat" (!!!)

 

[KeithG]

I did 6 night dives during the last Bonaire trip and replaced batteries only once.

You are not staying under long enough...

But seriously, you went through 2 sets of batteries in 1 dive trip. How can that be economical? I figure a set of rechargeables is good for at least 4 years with no issues. I still have a handful of 10 year old rechargeables that are used on a daily basis (keyboard wireless mouse, laptop wireless mouse, tv remote, roomba fence thingy,...).

 

[fmerkel]

Alkaline tend to have a linear discharge curve (voltage slowly but surely drops). Rechargeable drop a bit, then hang on for a long time before dropping precipitously.
Depending on the light driver the voltage may be supported for a steady output, or it may slowly drop. If supported alkaline will be OK. If not you are better off with NiMh.
This is totally ignoring the cost effectiveness issue.

 

[bergersau]

18650's and the like are Lithium Ion batteries. They hold charge for long periods and are good for hundreds of recharge cycles if well treated. (As evidenced by phone batteries.)
However they have different characteristics to Ni-Cad or Ni-Mh rechargeable batteries.

The key points with Li-Ion batteries are to always use 'protected cells', buy quality cells (NOT Ultrafire), use a quality charger designed specifically for Li-Po batteries and NEVER run them too flat.
Discharging these cells to below three volts damages the chemistry of the cell and can turn them into firebombs during the next charging cycle as evidenced by the spate of 'Hoverboard' fires in recent months. If you see the light start to dim in your flashlight - immediately turn off the light and check the battery voltage with a multimeter before recharging. If below 3v - recycle the battery and buy a new one!

Edit: Corrected Lithium Polymer to Lithium Ion as needed.

 

[BoltSnap]

I test my batteries periodically to confirm their capacity. All my 18650s test over 3000mAh and all my 26650s test over 5000mAh.

How do you test these specific batteries please? I have a sophisticated battery tester but it doesn't test these types.