Petzl Myo XP disaster: a word to the wise

A better move would have been to remove one or all. By flipping one, you upset the evil electrons that will impose their wrath upon the batteries, and quite possibly the circuit of the device too. Of all lessons to be learned, this one is pretty inexpensive. Consider it a bonus that you learned it at home instead of out in the backcountry.
Pour a drink and enjoy the rest of your weekend!

Along similar lines, another thing you should never do is absent mindedly put a battery in your pockets with loose change or other bits of meatal as that's a recipe for conductivity city and acid in your crotch…which is to be avoided to be sure.

I thoughtlessly put a pair of AAs in my pocket once, then, later that night, took my pants off at night and tossed them on the floor… The next morning one of the AAs had burst and there was a giant hole in the pants and even some burns on the carpet where they'd been tossed.

Not smart.

The backwards battery trick only works if you have an even number of batteries, and they are all at equal state of charge. Otherwise you are running current through the odd battery backwards, hence cooking it. Should not have happened if the headlamp was off, but then again the whole point was to protect against accidentally turning it on. Defeats the purpose if accidentally turning it on cooks the batteries anyway.

So I take it that I turned it on by accident, and that's what completed the circuit?

Can I trust the headlamp anymore??

Yikes, I guess you must have switched it on accidently, but being familiar with the XP's switchgear it's hard to guess how. I suppose closing the circuit created a Battery War, with the two cells facing off against one, with the results you experienced. (This is a very scientific speculation hat I'm wearing here.)

Either the headlamp works or it doesn't–there's no middle ground. Reversing polarity on an LED will kill it pronto. Luckily, the battery box is far away from the electronics so they didn't share in the heat event.

For anybody wanting a failsafe battery disconnect while keeping them in place in the flashlight, slip a little piece of cardboard or plastic between one of the batteries and a terminal–guaranteed dead circuit. Store it in the battery container between uses.

They have issued overheating warnings for them even when installed in proper order.

This is a quote from the REI site.
"Petzl warns against the use of lithium batteries with this headlamp as doing so might cause the lamp to overheat and damage the LED bulbs."

You may choose to use them but I don't know if Petzl's stance is widely known.

G'Day
Just a note on the XP with lithium batteries. I have one of these and use it nearly every day at home around my farm as well as hiking. I thought id try a set of expensive lithium batteries but i found they only lasted about half the life of normal HD batteries. I found no other problems though.
Darren

Yes I was aware of Petzl's stand on Lithiums. The problem is that modern Lithium batteries produce more current that the theoretical maximum spec for AA's. Since the Petzl circuitry is unregulated, this overcurrent situation can cook your LED. Petzl says it's not their fault, since it's technically a non-standard battery causing the problem.

Since I live in freakin' Canada, though, the headlamp is not worth bringing if it's going to dim out every time it gets cold out. My solution was to never run it on high power when the Lithiums were fresh, thereby theoretically preventing an overcurrent situation in the LED.

It was either that or throw it out, since I don't need all that light in the summertime!

Why not use a light designed to handle lithium batteries? There are a number of them out there.

I bought it before they issued the warning about Lithium batteries.

I traded emails with them about how my $70 winter headlamp was now useless in the winter, but they just insisted that it's the fault of the battery makers and they take no responsibility. I understand both sides of the issue.

I was kind of secretly hoping that I'd cooked mine through my little misadventure, but alas it still works.

The Complete Walker also disavows the use of lithium batteries with LED flashlights, saying they're not compatible. In cold weather I keep my batteries in a pocket (sans coins and keys) so they'll be warm, preventing the power from falling off so rapidly.

I have used lithium batteries in my Princeton Tec headlamps for a couple of years now without issue. However, I have never tried lining up all the batteries in the same direction! My current headlamp – the Princeton Tec Quad is voltage regulated, which would presumably solve the Petzl concerns.

NiMH cells perform well in the cold, and while their output is lower than fresh Li or alkaline cells, they should still perform adequately in the Myo. They're also vastly less expensive to run.

Fresh Li cells can put out 1.6V or so, and that's the risk they pose to an unregulated light (such as the Petzls). They're quite safe in the regulated PT lights, and are almost freakishly good in the Eos.

Of course, LED overheating wasn't the problem in the OP here. It was a case of battery self-destruction.

"I have used lithium batteries in my Princeton Tec headlamps for a couple of years now without issue."

Yep me too.

Ditto on Rick's observations re: the EOS.

Greetings BPL friends,

I've used the MYO XP for 3 years with Alkalines, Rechargeables and Lithiums. I LOVE this light, and have had no negative issues with it (NONE!). That is until it just plain stopped working about a year ago. I called Petzl, customer service said "send it up" and within the week a brand spankin' new one arrived via mail. Turns out there was/is a recall of some sort. I mention this to reflect a MOST EXCELLENT PETZL Customer Service experience!
However, while on one of the other outdoor gear websites discovered a new model, an update of the MYO XP. The MYO RXP. Was surprised and saddened to find that it does not come up at all on the BPL "search". If you like this headlamp, look into the updated version. I find the improvements highly desireable.
I am getting one !

TheThriftstoreMountaineer
USA

My understanding from correspondence with Petzl is that the problem with lithium AA batteries in the Myo XP is that these batteries can put out much higher currents than alkaline batteries. So, if the wires get worn and short out, quite a lot of energy is put out instantly. This can cause a fire or even an explosion. My solution is to inspect the wires and connections as the headlamp gets older and to replace or repair anything that could cause a short circuit. The same is true of the Tikka XP.

I don't think that the higher voltage of new lithiums will damage the circuitry but I could be wrong. I'll find out next winter.

I like both the Tikka XP and the Myo XP quite a bit.