When should I install a new battery in my EDC?

My EDC is a Fenix P1D Premium Q5. I've always used Duracell Ultra CR123 primary cells in this single-cell light and have been pleased with their power and longevity.

Use of my P1D varies tremendously depending on need. Sometimes it's on for 30 seconds in low mode to locate an item dropped under a restuarant table; other times it's on for 10 minutes in turbo mode to illuminate a dark walkway for a group of pedestrians. Sometimes it's not used for days; I have other lights for use in my home and my shop.

It's been a couple of months since I installed a new battery in my EDC, but my P1D still shines brightly; I haven't noticed any reduction in brightness.

Of course, I'd like to make sure my P1D is as ready as can be at all times by keeping a fresh battery in it, but I don't want to trash a Duracell that's still 90-95% good by replacing the battery every month or two "whether it needs it or not."

Is there consensus regarding when to replace batteries in an EDC light that gets only occasional use?

I have a digital multimeter. Should I test the battery weekly and replace it when it falls below a certain voltage? If so, what voltage?

All suggestions are appreciated.

Each person has his/her own ideas when it comes to this.

Don't use a multimeter since it does not test the cell under load. A cell could look great when tested using a multimeter, but when you apply a load to it, the voltage drops too low to be of any good. My idea is to test my cells from time to time with a ZDS tester which applies a load to cell equal to a flash from a camera. When it shows 0% - change the battery. Anything else you are OK, but you have some idea as to when you will need to replace your cell. Always carry a spare or two because you will never know when you will need it. Many people use a pill fob to carry a single CR123 in.

Carpenter said everything I was going to. I would go further and not only carry a spare battery but also a spare light, something with really long runtime and bright enough to work in a pinch. Having a spare battery on you means you can use your light until you notice it's performance has decreased significantly and then you can just swap it out.

CR123s last for roughly ten years when not in use, it will easily last many months with only occasional use. Fenix is reknown for excellent ruler-flat regulation, so your P1 will always have the exact same output so long as the battery is good. When you notice that it's dimmer than usual, that's the time to replace the battery - if possible, don't run it once it falls out of regulation, as this can put undue stress on the battery and cause various types of failures.

I feel your pain, not knowing the state of your batteries. I used to be concerned of having a mostly discharged battery in an emergency, but didn't want to waste batteries by throwing away partly discharged ones.

I solved the problem with rechargable CR123's and AAA's. Every month or so, or more often if the light was used heavily, I replace my partly discharged battery or batteries with a fresh one from the charger. That way I always have from 100% to about 80% capacity in my battery.

At work, I EDC a P1 CE and use it often. Although the battery will last for a couple of months with my short duration intermittent use, it goes from bright to off in moments when dead. Rather than change the battery on the spot, I use my Peak Matterhorn 3LED key chain light until its convenient to change the battery in the P1. I keep extra lights and batteries in my car.

Alternatively, in the darker months or when working a third shift, I belt carry a SF6P with a Malkoff as a third light.

i think that is a situation i am in too. i value runtime a lot and you never know when you need the full runtime from a battery. carrying an extra light or battery will be crumblesome cos all these things in the pockets (wallet, keys, flashlight, mobile phone, etc) will make a pair of trousers look like a loaded diaper i guess a lot of guys just like to go out empty handed, without an extra bag or such. :sigh:

I would suggest you carry a backup light in addition to your P1D. That way, you should never be without light, and is the perfect excuse to go get another light :naughty:.

Doesn't have to be anything flash, something like a photon clone can be had for $1 and can reside with your keys. If you want to splash out, there is always the L0D Q4.

I really appreciate all the advice presented here. Now I've got a more comments/questions:

1. Regarding the use of rechargable batteries, I believe I've read that rechargables don't work well in the Fenix P1D. From what I understand, the higher voltage of rechargables (3.7 volts) causes the P1D to ignore its ability to change output levels, and it works only in turbo mode when using rechargables. I know I can buy 3-volt rechargables, but others here have experienced low capacity and short run times with the 3-volt rechargables. Am I correct about this stuff?

2. I've been intrigued by the ZTS battery tester, but always thought, "I can buy a lot of CR123s for thirty bucks." So, is the ZTS tester a worthwhile investment? If I buy one, could I accurately determine when my P1D's battery has reached 50% capacity, for example? Have other CPFers had good results with the ZTS tester?

3. Carrying a spare battery is a good suggestion. I do keep a spare CR123 in a small, plastic holder in the pocket of my winter coat. Problem is, I don't wear my coat during the summer months, and I don't have room for another item in my already crowded pants pockets. But I will put a spare EDC battery in my car, for sure.

I have a light that I use for getting around the house at night, checking on the kids, etc. Since that is never for anything critical, I take the batteries out of my critical application lights and use them in this light. For the lights that I leave the house with, or want to have complete confidence in, I change them whenever know I've used it a bit, or can't recall when I changed it last. The partially used batteries from my critical lights get cycled down to my inside the house carry light where they get run into the ground.

I use an rcr and charge it up everyother day or day to day depending on usage and i also keep a spare primary in the car as well......

I wouldn't worry too much. As long as it fires on turbo, you are pretty much guaranteed at least a couple hours on low still. When the light can no longer fire on turbo anymore, it's time to change.

There are 3.2v and 3.0v RCR123s, I'm not sure how they work with the P1D-CE though.

IIRC the 3.2v(3.0v?) LiFePo batteries have a lower capacity but the 3.6v Li-ion batteries with a circuit to drop the voltage to 3.0v have the same /similar capacity ratings as the 3.6v Li-ion batteries. Both have less capacity then a primary battery.

If you can't carry a spare battery, maybe a small spare light could work.

Exit32 said:

2. I've been intrigued by the ZTS battery tester, but always thought, "I can buy a lot of CR123s for thirty bucks." So, is the ZTS tester a worthwhile investment? If I buy one, could I accurately determine when my P1D's battery has reached 50% capacity, for example? Have other CPFers had good results with the ZTS tester?

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If you are using single cell lights as described above, then the only use you will get from a ZTS tester is knowing how much capacity is left in your cell. The ZTS tester really shines when you start getting into multiple cell lights. CR123's MUST match capacity when you put them in a light. If not, you could start something called a back charge which may lead to a condition called "Massive vent with flame". Search CPF for some examples of what the results of that condition do to a light. Not trying to scare you but I always check even new cells to make sure they are at the same capacity before putting them into multi-cell lights.

To answer your question, a ZTS tester shows results in 20% increments (0% no light - 20% - 40% - 60% - 80% - 100%). I personally have had good results with the ZTS mini. Not only does it test CR123's but also Alkaline 1.5 & 9 volt batteries as well as other not so popular formats such as CR2.

Exit32 said:

I believe I've read that rechargables don't work well in the Fenix P1D. From what I understand, the higher voltage of rechargables (3.7 volts) causes the P1D to ignore its ability to change output levels, and it works only in turbo mode when using rechargables.

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I keep a RCR123 in my P1DCE and here are a few observations:

1. It works very well, in a way.

2. It still changes 'output levels', but all the levels are equally bright until the voltage of the RCR drops a good bit. You still have to cycle through primary-high-low to get to strobe but all will be the same relative output.

3. The light gets pretty warm with a RCR when running for more than a minute or two, but this is also true on 'high' with a primary battery.

4. I don't miss the lower levels(primary, low) one bit.

While I love the P1D's form size/brightness, I don't like the three light levels. High isn't even twice the output of primary and low really isn't all that low. I use my P1D with RCR as a very bright, single mode light, P1 style. I like the simplicity of an 'on/off', very bright, very tiny light.

When I want a much lower 'low' as I often do, I use my keychain light(Liteflux LF2).

Check out Chevrofreak's excellent runtime graphs of the P1D-CE using RCRs:

http://lights.chevrofreak.com/runtimes/Fenix%20P1D%20series/Fenix%20P1D%20CE/

I wouldn't mess about with 3v rechargeables. Its not worth having the 'not so very low' for the very much shortened runtimes.

If you are so inclined, get a couple of RCRs. 'Top-off' the cell after any significant use and you'll always have 'fresh' power. For my money AW's are the best. Try them out in your P1D and see if you can live with the single output level. If not, go back to primarys.

My rule for changing out primarys when I used them in the light: When you change from 'high' to 'low' and you CAN'T see a significant difference in brightness, time to chuck the old cell. When the voltage drops too low, your modes become 'low-low-low', much like with the RCR they work as 'high-high-high'.

Whichever way you run the P1D, its a dandy little light, enjoy!

I went through these same issues with my P1D (with Leef body) I used to EDC. I tried rechargeables, but I lost multi-levels and the cell protection circuit would cause the light to go out without warning. I ended up switching to a Jet Beam CLE using a AA Eneloop which top off about once a week. I just couldn't bear throwing away half used CR123 cells.

A concept I thought about but haven't found a way to impliment it yet until the D10 and EX10 with Piston Drive. How about a 2 cell version of these lights. One of the cells would be isolated and carried as a spare until needed. Then just swap positions when the primary runs out. Anyone want to take this on to a reality? I love my EX10 but would like it even better if it was a 2 or 3 cell version.

There is no benefit of keeping a spare cell inside of your light. You would get MORE than double the runtime if you use them both together, instead of separate.

Exit32 said:

3. Carrying a spare battery is a good suggestion. I do keep a spare CR123 in a small, plastic holder in the pocket of my winter coat. Problem is, I don't wear my coat during the summer months, and I don't have room for another item in my already crowded pants pockets. But I will put a spare EDC battery in my car, for sure.

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I ALWAYS carry an extra cell for whatever light(s) that I carry daily. I just roll them up in plastic wrap and tape them closed. They don't take up much room and I ALWAYS carry a Photon II DS/2032 to light my battery changes. That's the best you can do is carry a spare batt. and a spare light!

GPB said:

I have a light that I use for getting around the house at night, checking on the kids, etc. Since that is never for anything critical, I take the batteries out of my critical application lights and use them in this light. For the lights that I leave the house with, or want to have complete confidence in, I change them whenever know I've used it a bit, or can't recall when I changed it last. The partially used batteries from my critical lights get cycled down to my inside the house carry light where they get run into the ground.

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This is what I do as well. But, I do always have a backup flashlight on me as well! Plus a couple more in the car.......