Companion blog: Adventures In Stoving

Saturday, September 24, 2022

To Change a (PLB) Battery

I want to share my experience of how "stupid easy" (as one friend put it) it is to change a battery on a Personal Locator Beacon (PLB).  I'll also share the story of the incident that made me buy a PLB.

Clarification:  This post is not meant to champion PLB's over commercial satellite communication devices (InReach, SPOT, Zoleo, Bivy Stick, etc.).  PLB's and commercial satellite communication devices both have their pros and cons.  Yes, you can compare them, but there are fundamental differences.  If you'd like me to weigh the pros and cons, I'd be happy to, in a separate post.  If that's of interest, then maybe put a comment below to that effect.  I definitely have recommendations for some specific cases (remote areas, tight budget, deep canyons, etc.), but, in the general case, I will take no ultimate position.

My ACR brand ResQLink personal locator beacon (PLB).
The specific model I have is the PLB-375.

But first, some background.  You can skip the next two sections if you already know all this.

What is a PLB?
A PLB is basically a satellite distress beacon.  If one gets into trouble in a remote area where there is no cell service, one can activate a PLB, and a 406 MHz distress signal with GPS coordinates will be sent to a satellite in orbit around the earth.  When the satellite detects the distress signal, the appropriate authorities will be notified.  If you're in the United States, typically the US Air Force Rescue Coordination Center would be notified if you're on land, and the US Coast Guard would be notified if you're at sea.  

The overall program is run by the National Oceanographic and Atmospheric Administration (NOAA) in the US.  The program was originally developed for ships at sea, expanded to aviation, and finally expanded to include private individuals such as hikers, backcountry skiers, snow mobile enthusiasts, hunters, etc. I mention NOAA just to emphasize the fact that a PLB is part of a multi-national government backed program.

A PLB is different from a commercial satellite messenger service such as InReach, SPOT, Bivy Stick, Zoleo, etc.  Satellite messenger services work off of satellites of either the Global Star or Iridium commercial satellite networks.  A PLB works off of a constellation of COSPAS/SARSAT satellites put into orbit by the United States, Russia, the European Space Agency, and India (that I know of; perhaps there are other nations who have become part of the program).

Why a PLB -- a brush with death.
About eight or so years ago, a friend of mine was doing some solo snow shoeing near San Jacinto Peak (10,834' / 3302m).  She slipped on some ice and whacked her ankle against a tree.  She couldn't get up; she had fractured her ankle.  She was alone,  injured, and darkness was fast approaching.  This friend of mine is made of stern stuff.  She hauled herself uphill in the snow with a broken ankle.  No, this is not your dad going on about "When I was a boy, it was uphill both ways to school in two feet of snow..."  Seriously.  She climbed uphill in the snow on her hands and knees with a broken ankle.  No offense intended to my friend, but I'm glad it was her and not me; I'd be dead.  

Why uphill?  There's a small stone hut built by the Civilian Conservation Corps in the 1930's near the summit of San Jacinto Peak.  Using her snow shoe as a a shovel, she dug out the snow blocking the front door (told you my friend was tough) and crawled inside.  That night, a storm struck.  Outside, the storm raged.  Inside, my friend shivered miserably in the unheated stone hut, but she was alive.  Had she been outside, she'd have been dead.  

Now, if you know anything about winter survival, shivering is the first stage of hypothermia.  Hypothermia results when your internal body temperature drops below normal, which is about 98.7F / 37C.  Once one's internal body temperature drops below a certain point, one loses control of one's mind and body.  If hypothermia progresses, it can quickly lead to death.  Yes, my friend was alive, but she was in serious trouble.

The next day, she didn't show up for a brunch, and she was reported missing.  Note that she's been injured and stranded on the mountain for nearly 24 hours by this point.  By the way, it's a really a good idea to have a designated person to check in with after a hike.  Your check in person should know to contact Search and Rescue (SAR), if you don't check in by a certain pre-arranged time.

Normally, SAR responds quickly, but on day two of my friend's ordeal, the storm was still hitting the mountain.  It's neither safe nor practical to search for a missing person in a storm.  My friend spent another night in the hut, shivering, again risking hypothermia and death.

Finally, on the third day, the storm abated, and SAR got out on the mountain.  They searched a number of likely locations, including the summit hut, to which a helicopter with rescuers was dispatched.  My friend remarked that hearing that chopper was the most beautiful sound she had ever heard.

Now, why do I relate this story here?  Think about it. If she had a PLB, she could have:

  • Immediately notified people she was in trouble (recall that it wasn't until the next day that she was reported missing)
  • Immediately reported her location (recall that GPS coordinates are embedded in the distress signal).
SAR might have been able to go right to her and bail her out the same day she was injured rather than days later. 

I had been thinking about buying a PLB, but I had been on the fence.  I mean the stinkin' things were over $400 at that time!  If she had a PLB, my friend might not have spent two nights in a freezing stone hut, potentially risking death.  I was sold.  In 2013, I bought an ACR ResQlink PLB (model PLB-375) with a stated battery life of six years.

Batteries are expensive -- or are  they?  
I had read that changing the battery on a PLB was expensive, nearly the cost of a new unit.  When my battery expired in 2019, I didn't even consider getting a new battery.  Instead, I bought an InReach.  A commercial InReach is reputed to be less reliable than a government backed PLB, but, on the other hand, an InReach is clearly more versatile than a PLB.  An InReach is two way custom text or email and can be used in less-than-emergency conditions whereas a PLB is one way communication without any message (other than the unit number and the GPS coordination) and is only for emergencies.  I figured the greater versatility of an InReach was worth it -- and that it wasn't worth paying nearly the price of a new unit to replace the battery of my PLB.  But does it really cost nearly the price of a brand new unit to replace the battery?

The real cost of a new battery
Well, I guess things had changed since I bought the unit.  A friend alerted to be to the fact that a replacement battery could be had for just $40 and that replacement was so simple that you could do it yourself!  The original recommendation was that only a trained technician should change a PLB battery.  

Forty bucks!  Well, shoot, that's not bad for a unit worth over $400, a unit already paid for, a unit in near-perfect condition.  I decided to buy and change the battery on my own.  If you scroll all the way down to the bottom of this post, I'll list the website address (URL) of where I got my battery.  I don't want to appear to endorse or be connected to any company, so I won't put the address here.

Changing the battery
The back of the unit is held on by two simple Phillips head screws.
The back of my PLB.  Note the ordinary Phillips head screw at the bottom of the photo.

One simply unscrews the two screws and takes the back off.  Inside was my original battery pack, stamped with the expiration date "01/2019."  

Important:  Note the position of the red and black wires.  They cross the body of the PLB leading away from the plug.  When disassembling your PLB, be sure to take careful note of where these wires are and where they go in relationship to the two little grooves on the main body of the PLB.  The back of the PLB has a protrusion that fits into the two grooves.  The wires go to the right (as oriented in the below photo) of the groves, toward the battery.
My original battery pack inside my PLB

There's a warning on the back of the battery pack that only "OEM" parts (i.e. parts from the original equipment manufacturer) should be used when replacing the battery -- and then only by a trained professional.  But is this really rocket science?
The warning on the back of my original battery pack

Examining the battery pack, I noticed that it was just a series of three ordinary CR123A lithium batteries, wired together, the kind you can buy from ordinary hardware, sporting goods, and other stores.  Now, they are specially wired together, so you can't just go and buy some batteries from the local store, but there's nothing so esoteric here that a specialist would be required to handle it.

Looking at my new battery pack from the side. 
You can see that it is just an ordinary CR123A battery.

I unplugged the old battery pack and plugged in the new battery pack.  The plug was a little smaller, but it wasn't any more complicated than unplugging, say, a blender (or similar) at home.  You can see the little white plug in the photo, above.  After that, I spread some silicon grease on the gasket of my PLB, put the cover back onto the unit, and screwed in the two Phillips head screws.  I ran both the quick internal test as well as a full GPS test.  Both tests were successful.  

In short, it's just this:
  1. Unscrew the and remove the back cover.
  2. Unplug and remove the old battery pack.
  3. Plug in and emplace the new battery pack.
  4. Replace the back cover and fasten the two screws.
That's it.  That's all there is.  It's really not that much more than changing a flashlight battery.  Optionally, you could put some silicone grease on the gasket to ensure a good seal, but that's hardly rocket science.

Battery Life
But one question was still bugging me.  Just how much charge was left in the old batteries?  Was it really necessary to replace the battery after just six years?  Isn't the shelf life of a CR123A battery supposed to be ten years?  I pulled out my trusty Radio Shack battery tester.  I was about to find out!

First, I cut apart the shrink wrap holding together the old batteries.  Then I broke apart the batteries where they had been glued together.  Finally I pulled off the wiring between the batteries.
The batteries with the shrink wrap removed.  Note the wiring.

What did I find?  The old batteries still had a charge in the "good" range.  Note carefully the position of the needle in the photo, below.  It's on the left side of the first "O" in "good."  Be sure to look at the middle scale which is for lithium.
The charge level on one of the old batteries.  Be sure to look at the middle scale, the one for lithium.  The charge level is just to the left of the first "O" in "GOOD."

Then, below, is a photo of the charge level of a new battery I just took out of the packaging.  Look at the middle scale, the one for lithium.  It's ever so slightly higher than the previous reading from the old battery.  Now, in fairness, the battery I pulled from my battery collection is one that I've had for a while.  A fresh one from the store might have a higher charge.  If I get a chance, I'll buy a brand new battery, test it, and update this blog post.

The charge level on a new CR123A battery, freshly opened.  Look at the middle scale.  The charge is  just slightly higher on the new battery, but the difference is almost indiscernible.

Now, I'm not advocating skipping battery replacement.  I'm just noting that you might get more life out of your PLB's batteries than the stated six years.  Maybe.  Of course that would depend on how often you test.  I don't test often.  Basically, I test once at the beginning of each backpacking season, typically around Memorial Day weekend, and that's it.  If you test every week (which seems ridiculous to me) or before every trip, maybe your battery won't last as long.  My main point is:  Don't assume that a PLB past its expiration is useless.  I'd still carry it even if I had not yet had the opportunity to buy a new battery pack.  Chances are it will work past the expiration date.  

Even if a PLB in use were to die before it's stated 24 hour operating lifespan, you'd at least have notified the authorities and given them your position.  Remember that the rescue coordination center is going to try to call the contacts you listed when you registered your PLB.  If your check in person says, "yes, so-and-so is definitely out there," then they're going to dispatch a SAR team.  If the signal stopped after several hours, the SAR team is still going to be sent out if they've confirmed that you're out in the wilderness.  This is a good argument to register your PLB and keep your registration current -- that's the only way they know who they're looking for.  In the case of my friend, as soon as SAR found out that she knew of the summit hut, they immediately sent a helicopter, and she was rescued.

Reduce, reuse, recycle!
Regardless of how long you wait (or don't) to change the batteries, don't throw away the old ones!  They're perfectly good CR123A batteries that can be used for other things like flashlights, headlamps, etc.  I put mine in my headlamp, and it fired right up.

OK, that's it.  That's all there is to changing the battery.  It's really not a big deal, and it should give your PLB another six years of life -- for maybe 10% of the cost of buying a new unit.  If you spread $40 out over the six year life of the battery, the cost is less than $7 per year.  I pay $12 per month for the lowest level of service for my InReach.

Happy hiking,


P.S.  If I have both an InReach and a PLB, do I plan to carry both?  No.  I plan to carry the InReach, and I plan to have my daughter carry the PLB.  If, God forbid, we ever became separated, then she would still have a way to get help.  If we were together and I couldn't get a message out on the InReach, then we'd have the PLB to fall back on.  

There are definitely times where I have not been able to get a message out on my InReach.  Once, when I was doing some backpacking down in the bottom of a fairly deep canyon, I couldn't get a message out until the following day, maybe 18 hours later.  That's atypical, but it does happen.  The majority of InReach messages go out in less than 15 minutes; sometimes they go out almost instantly.

P.P.S.  People have asked, so I'll say it:  I got my battery at  However, let me be clear.  I make no endorsement of, nor am I affiliated with, nor am I compensated by any manufacturer.  My experience with them has been good so far, but I don't have any long term experience with them at this juncture.  Caveat emptor.


  1. Great to see you fire up the ol' blog again, HJ! I have the same PLB as you. Did you go with beaconbatteryreplacement for the new pack? Thx (aka stbrnnr on other platforms on which we've interacted)

    1. Yes, I got my battery from Beacon Battery Replacement. Maybe I should have said that, but I'm sensitive about appearing to endorse or be connected to any particular business.

      UPDATE: I have now added a link to Beacon Battery Replacement.