How to change the battery on a Casio ProTrek Solar Powered watch

In my opinion it shouldn’t be necessary to change the battery on a solar powered watch for obvious reasons but searching on teh internet it seems that these watches are prone to battery failure. The battery is a Cobalt Titanium Lithium Rechargeable battery CTL1616 made by Panasonic and also SONY. Mine has already been replaced under waranty but when it failed again less than two years later Casio wanted more to change it than I can buy a new watch so I decided to do it myself.
First remove the strap by using a pin to compress the two pins in the usual way for any watch.

Now remove the four screws and take the back off


remove the rubber sheet to expose the battery cover, note this is not the battery but a sheet metal cover


Inser a needle into the cavity at the 12 o clock position and release the metal clip so the cover can be lifted and the battery slid out as shown in next photo


Slide the battery out. My battery had brown ooze at the join which doesn’t look healthy.


Put your new battery in observing polarity.

I found a link online for a comany that can supply them it is or get there from  BTW I have no connection with either company, information only.


Update : –  I fitted a non-rechargeable battery last October cost 20 pence on ebay (pack of 5 for £1) and it is still going strong with a “full charge” showing on the display after nearly a year of use

Summary: I wouldn’t bother with the expensive rechargeable CTL1616 when you can get this performance from a throwaway replacement cell.

Here is some data for the battery below for those that are interested





Nominal Capacity 18mAh


Nominal Voltage 2.3V


Standard Discharge Condition 1.0mA


Standard Charge Condition
(Constant Voltage and Constant Current Method)
Voltage 2.6V
Current 3.0mA
Time 24h


Cathode Active Material Lithium Cobalt Oxide


Anode Active Material Lithium Titanium Oxide


Energy Density per Volume 129Wh/l


Energy Density per Mass 38Wh/kg


Cycle characteristics(100%DOD)* More than 100 cycles


Operating temperature range -10~60�C


Weight 1.1g
* More than 70% capacity
discharge capacity versus load current

discharge capacity versus load current

Charge Characteristics

Charge Characteristics

more graphical data in the gallery below



49 Responses to “How to change the battery on a Casio ProTrek Solar Powered watch”

  1. Very nice and usefull information, many thanks for sharing..!

  2. Glad you found it useful, thanks for the kind remark 🙂

  3. Aha! looks like an answer to my watch problem. Bought my watch some years ago, now out of warranty. I rarely wear it, (A) because of damaging it at work. (B) Mobile phones, PDA, Blackberry all have time functions, and the need for Casio time is not required.

    With my watch, the light, digital compass and altimeter do not work. Battery shows full strength.

    Do you it is worth a battery change?

  4. Thanks for reply. Didn’t bother with a 50 Pence battery, just bought a new CLT1616 and changed it over. Did the job, and all functions working that I can test at this time of night! Day charging will bring it back to peak performance. Thanks again.
    And watch out for those springs!

  5. Hi,
    My Protrek recently have “open” displaying on what it use to be the date. Doyou think this because the battery is exhausted?

  6. Harry, it sounds like you have left the back off the watch or it has been re-assembled without one of the tiny springs properly in place. As soon as you open the watch ‘open’ appears on the screen, as long as all the small springs are still in place when you close the watch ‘open’ should disappear. Hope this helps. Geoff

  7. Jamesatleast Says:

    I have a casio protrek1300 and I replace the battery wich is new.
    The replacement it was made as I see on pictures.
    The watch don’t starts yet.
    Please make my happy and tell me what’s up!!
    Thank’s, very much!!

    • I would check that the battery is the correct thickness, in the right way round and making contact both sides.
      If this all seems OK I would check the battery voltage with a digital multimeter before refitting.

  8. CIAO

  9. Peter Lee Says:

    Hi, What is the model of the non-rechargeable battery that you used to replace CLT1616. Is it CR1616 (or ECR1616, DL1616) which is a 3V Battery ?

  10. Update from GTOUSER, it’s now over a year since I replaced the rechargeable battery with the ordinary non-rechargeable 20 pence CR1616 and it’s still going strong with 6 segments lit on the battery condition indicator meaning “full charge”

  11. The strap for my watch is starting to crack now; does anyone know of a cheap source for these? I have seen them for about £15 but that seems a bit steep for a piece of plastic.

  12. Thanks! Just done the battery swap on mine and all working beautifully. I’d add that removing the strap isn’t strictly necessary though – getting it back on was more of a fiddle than doing the battery swap.

  13. You UK guys are tops. Terrific help on the watch.

  14. Hi, my CTL1616 ran out and I’d like to put a CR1616 in my OCW-520TDE, but what about the charge? may the CR1616 be damaged by applying a charge current ?

  15. Hi Nick
    Well it is now about 18 months since I fitted a CR1616 to my watch and it is still going strong with 6 segments lit on the charge indicator. I think that in practice what will happen is that any charge current is consumed by the watch. The solar cell does not seem to have enough “oomph” to damage the battery.

  16. T.C.Woo Says:

    Hi Gtouser,

    Do you have any experience in changing battery for water resistant watches?

    • gtouser Says:

      Yes the watch in the article is water resistant. Just be careful that any O ring is in place and undamaged and clean. You can put some silicone grease on it too when you refit it.

  17. James Fong Says:

    May i know the battery model for Casio Protrek PRG 80T? and it is the same procedure to change the battery shown on this place? Because the back of the watch seem deferent from the picture shown

  18. There is no need to remove the watch strap as you can easily slide the back plate from between the straps.
    I would be very reluctant to fit a non genuine battery to an expensive watch such as this, false economy.

    • gtouser Says:

      Hi Gavin
      It is necessary to remove the straps on the Protrek because they cover the screws, or are you talking about the PRG80T?

  19. Anonymous Says:

    It’s actually a nice and helpful piece of info. I’m
    happy that you shared this useful information with us.
    Please keep us up to date like this. Thanks
    for sharing.

  20. Tim Spencer Says:

    I used these instructions to change the battery on my PRG-80T – good stuff. The only thing missing is the reset procedure, which needs to be done once the battery is replaced (at least on the PRG-80). If this isn’t done, then the display just flashes away when you’ve put the watch back plate on, and the buttons don’t work. There is a gold contact in a hole in the exposed metal plate beside the letters ‘AC’, and another contact directly on the same plate next to a (-) mark. These contacts have to be connected with a piece of metal for 2 seconds (I used an unwound paper clip). As soon as that is done, the watch is available for setting up once the back plate is replaced.

    • you are my hero. Replaced battery, watch showed time, but no control buttons worked. No where else was a reset mentioned. After opening back 5 times, putting back original battery, and ready to throw watch away, saw this entry. Reset worked a charm.
      Anyone else trying this:
      First, be very aware of the three tiny springs that are exposed when opening the back. Do not let them escape.
      Second, there seem to be different models of this watch. Battery holder on my watch was totally different than one pictured.
      Third, do the reset before closing the watch.

  21. Daniel Weiler Says:

    thanks ever so much. where can i get the specs for a new O ring or can i stay with the old one? a

    • Well I reused mine because it was in good condition and I had some silicone grease which I applied to it to assist with the sealing. If I had a new one I would probably fit it as it is good practice.
      Inspect it with a magnifying glass for nicks and most importantly clean out the channel that it sits in with ethanol or similar, do this even if you fit a new o-ring. You could measure the o-ring cord diameter with a micrometer and also the diameter of the channel with a vernier calipers to determine the sizes if you want to replace it. You can probably get o-rings on ebay once you determine the sizes.
      If you want to reuse a distored but otherwise OK o-ring you can drop it in a cup of boiling water for a few minutes and it will often give it a new lease of life. So to summarize, ideally you should replace it but if you enjoy improvising like I do you can often make it work OK by cleaning it and applying some preferably silicone grease or second best petroleum jelly (vaseline).

  22. christopher suleske Says:

    Thank you. I re-found my PRG-60T and remembered why I didn’t earlier change the battery: seemed silly to spend so much on an old watch I obviously didn’t need. I too thought of replacing it with a simple 3V lithium battery, but was dissuaded by several comments from people who seemed to know what they were talking about. They suggested the difference between 2.3v and 3.0v is substantial enough to cause problems, even ruin the watch. It seems like you’ve countered that with experience. If there were more room in the watch, I’d simply fit a small diode inline with the 3.0v battery. The 0.7v drop would give exactly the 2.3v the watch is expecting. It would also prevent the charge current from entering the battery.

    I will try your fix and if it doesn’t work – no big loss. Thanks again.

  23. Very useful ! My son nearly jumped over the moon with excitement



  24. Is all the above applicable to PRO TEK 2872 PRG-70?
    Thanks for very professional explanation! I can get to the tops of the pins with a great deal of difficulty. Is this normal? Your watch depicted , looks a bit different to mine. Many thanks again from a 78 year old living in South Africa!

  25. My PRG-50 show fully charged, but error message when i press compass, and the light dont lit up. Do you think i need to change the battery? Thanks in advance

    • Yes it’s worth a try. If the battery has deteriorated it might have a high internal resistance and therefore not be able to deliver power when given a heavy load.

  26. Hi, good blog, and detailed info, well done. I am using the information to try and put an ordinary 1.5v battery in my Pulsar Solar. I have however read many times about the danger of doing this, many blogs say the battery will explode!! What do you think?

  27. My pro trek shown low power wat i do

  28. My brother suggested I might like this website.
    He was entirely right. This post actually made my day.
    You can not imagine just how much time I had spent for this
    info! Thanks!

  29. Kris Dwornik Says:

    Interesting – I must be the lucky one. I bought a PRG70-YT about 12 years ago; I virtually NEVER took it off – at work, car maintenance, swimming, skiing, whatever. Totally faultless – until it recently had a ‘processor lockup’ computer style which was not a cost effective repair.

    However as I couldn’t bear the thought of losing it, about 5 years ago I bought another 2 year old immaculate one used by a climber. That one’s been in the box for 5 YEARS, taken out 3-4 times only to check for only a few minutes at a time – at it was STILL running in hibernation mode!

    Obviously I’m using that one now but have just bought another for when/if ??????????????? And I have the cheaper came one with the plastic strap for ‘if’ I feel guilty mechanicing – or maybe put the mechanism in the original Titanium case?

  30. Kris Dwornik Says:

    Just checked and the CTL1616 battery is as low as £12-65 on Ebay now.

  31. Thank you so much, you are amazing!

  32. tredlevel. Says:

    Hi, I own a pro trek PRG-80YT 1.. had it at least since 2005 or before? and its still on the same battery!! still going strong and in great condition..I must be lucky.

  33. David Bennett Says:

    I have a Casio Pro Trek PRT 40BV but the batteries need replacing Would you know the make or model number of the battery. There are two of them, quite thick and small. I have no idea were to buy them from. Thanks.

  34. Fine way of explaining, and pleasant post to obtain data on the topic of my presentation subject, which
    i am going to deliver in school.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: