Re: Heliotek HTE-1 rev.2 review - flashlightreview
OK, I heard back from Energizer, DuraCell and Battery Station on the safety issues quoted by Heliotek. As expected, Energizer was quite in support of their statements, while DuraCell and Battery Station were cautiously skeptical. In addition, these latter two cited Energizer making threatening phone calls of litigation for violation of their patents, which DuraCell and Battery Station affirm do not exist.
Energizer and DuraCell sent me a MSDS and technology report on their lithium and NiMH batteries. Battery Station did not send reports for any kind of battery, so I will leave them out of the following. Here's what I discovered:
The thermal governors exist in both brands, operating in the same rated temperature range. The useful temperature range is identical. The voltage and mAh are identical. The chemical structure is a bit different in the lithium compound.
If there is a noticable difference, it is in the mechanics of the pressure relief system. Energizer uses a ball and leaf spring, which will, if necessary, raise the edges of the positive end of the batter to allow gas/fluid to escape until pressure is adequately reduced. Then it seals itself again.
DuraCell, however, uses a thin plastic disc under the anode, and the anode itself has a "tooth" that is bent inwards, pointing at this plastic disc. If pressure builds too high, the disc rises, pushes against the "tooth" and it is punctured. Pressure is thus relieved, but the puncture is permenant. All gas and fluid will leak from the battery as it will not reseal itself.
Now, with that said, let us understand that any pressure venting would occur at temperatures above boiling point. The stated maximum operating temp of the Heliotek is 115F. The stated warranty is voided if the light is exposed to temperatures over 150F. The batteries carry a warning not to exposed them above 140F.
I therefore conclude, and this is my own judgement for my own light and my own safety, that DuraCell is a viable alternative. Given I won't be standing in a boiling cauldron at night (at least I hope I won't), and given that in hot Texas sun a car's interior can reach 180F and therefore I would NEVER leave ANY battery-powered device in my car, I see no reason I can't use DuraCell if they should offer a better price at any given moment.
Now, as to NiMH, something very, very interesting turned up in both the reports from Energizer and DuraCell. As it turns out, while their initial voltage is nominally 1.25 volts, their power delivery graph is the same shape as both companies' lithiums. In fact, both reports clearly state this in words.
Also, both reports state the pressure venting characteristics are identical to their lithium batteries.
Also, both state a maximum temperature exposure of 140F for both their lithiums and their NiMH.
NiMH has one caution that does not exist in the lithium documents, and that is related to hydrogen production.
I had long known that NiMH does NOT, repeat, does NOT produce hydrogen during its normal use of serving energy. Quite the opposite, in fact; hydrogen is produced, and then absorbed into the internal components, during CHARGING. During discharge, the hydrogen is desorbed and mixes with the peroxide, turning into water.
What I did not know was this one exception to the above, and only if the user makes this mistake. All batteries in the unit, if NiMH is used at all, must be NiMH. Further, all batteries must be of the same capacity in mHa (e.g., all should be 1800, or 2000, or 2300 mHa). A violation of this arrangement COULD LEAD TO SELF-OVER-CHARGING INSIDE THE UNIT, AND THEREFORE LEAD TO THE LEAKAGE OF HYDROGEN GAS OR TO AN EXPLOSION.
The reason is quite simple, now that I think on it. If you place an 1800 and 2300 battery together, the potential in the 2300 is going to want to flow to the 1800. The 1800 simply cannot hold any more than 1800. In chemical terms, it means that the water is being turned into peroxide, and the free atom of hydrogen simply cannot be absorbed into the nickle alloy. It remains free, and as more and more hydrogen is produced, pressure builds up. The 2300 will continue to discharge until it reaches 1800 mHa, and the 1800 will continue to build-up hydrogen gas. If enough gas is built up, leakage or explosion occurs.
However, with two 1800 or two 2300, the problem does not occur, even if one battery is not as well charged as the other. Charging inside the light might take place, but the lesser-charged battery will have no problem absorbing any free hydrogen. The net result is, if given a few hours to settle down, both batteries equal-out to an identical charge, which is something less than full charge.
So I again conclude that, at least for Energizer and DuraCell, NiMH is perfectly safe to use. I had not known about the potential for these batteries to charge each other inside a device, but given the technical explantion, I must leave it up to me to be careful about using the same mHa batteries. And again, this is my own opinion about my own Heliotek and my own safety.
One final comment on the pressure relief of NiMH; this, too, occurs above the boiling point. This, too, would seem to be rather rediculous in a statement about useful ranges of temperature. However, just so everyone is aware of the risk...
Charging produces heat. Quite a bit, actually. A slow charger may lead you to believe it does not, but in fact, the heat being produced is escaping to the atmosphere, and the batteries will feel cool to the touch. If you use a rapid charger, you can feel how warm the batteries are. Therefore, if you're inclined to try NiMH, and also leave this light in your car in the direct sunlight during summer, be aware that the 180F interior temp of your car, plus any accidental charging occuring between the batteries (if you mixed the capacities), COULD CAUSE THE BATTERY TEMPERATURE TO RISE TO THE PRESSURE RELIEF POINT, LEAKING HYDROGEN INTO YOUR LIGHT, AND CREATING A FIRE AND/OR EXPLOSION HAZARD.
Well, those are my finding and my thoughts. Just to make sure I don't get sued by someone claiming I TOLD them to use something other than Energizer L91 in their Heliotek, let me make it perfectly clear: I am NOT TELLING you to do any such thing. If you choose to use something else, I've given you some technical data on DuraCell lithiums and NiMH from both DuraCell and Energizer to help you reach YOUR OWN conclusions. Whatever you do with this information is, of course, YOUR OWN DESCISION. If you feel something could or will go wrong, then I advise you to stick with Heliotek's claims. If Energizer stops making the L91, then you will have to go back to Heliotek and see if you can get your money back, or convince them to extend their warranty to other batteries.
As for me, I'll be using NiMH on land, and whatever is the cheapest lithium I can find when I'm underwater...
Cheers!
Pond Jumper
