Petrel/NERD Battery Cap Improvements

To improve the sealing performance and O-ring life span, the battery compartment O-ring gland design has been changed from a crushed gland to a radial gland. Identification of the new radial cap can be made by observing the differences in the following table:


New: Radial Cap

  • Radial gland design
  • O-ring seals before computer turns on
  • Sealing NOT dependent on torque applied to battery cap
  • The compression on the O-ring is set by the gland groove diameter
  • Petrel computer marked with “RC” under strap
  • NERD computer marked with “RC” above battery compartment


Note Screw Head Height and O-Ring Colour


Note O-Ring Groove Style

Machine Screw: Pan Head #4-40 x 1/4” Torx T10

Machine Screw: Pan Head #4-40 x 1/4” Torx T10


Old: Crushed Cap

  • Crushed O-ring gland design
  • O-ring starts to seal as computer turns on
  • Sealing dependent on torque applied to cap
  • As the cap is tightened the O-ring is compressed into a cone shaped gland
  • Tighter the cap is the more the O-ring is crushed/compressed



Note Screw Head Height and O-Ring Colour


Note O-Ring Groove Style

Plastite Screw 48-2 Flat Head #4-20 x 3/8” Torx T8

Plastite Screw 48-2 Flat Head #4-20 x 3/8” Torx T8


12 Responses

  1. Do I get the replacement for free or do I have to order the new part?

    • Avatar Shearwater Research

      Hi Marco,
      There is no need to replace your battery cap for a new one unless you already had an issue with it.
      The old cap is still fine you just need to make sure you’re tightening it completely to prevent leaks.
      If you want to order a new cap in the future you just need to specify what kind of computer you have so you don’t wind up with the wrong one.
      Hope this helps,
      Shearwater Research

  2. Is this a replacement for Petrel 2 models also?

    • Avatar Shearwater Research

      Hi Andre,
      This isn’t a replacement for the old cap, we’ve just updated the design and we don’t want people ordering the wrong cap by accident. You can tell if your Petrel 2 has the new cap by checking to see if you have the blue o-ring and the “RC” under the straps.
      Shearwater Research

  3. I assume that this new cap will not work with a Petrel 1. Will there still be replacement O rings available for the Petrel 1.
    I ask this since the dealer I bought my computer from in Edmonton Alberta is no longer in existance.

    • Avatar Shearwater Research

      There will still be replacement o rings and battery caps for existing Petrels. Any dealer can supply you with them or you can contact us direct for assistance.

    • Avatar Shearwater Research

      Hi Pete,
      Thanks for letting us know.
      We’ll go check this out.
      Shearwater Research

  4. I have a petrel 1 as a backup to my petrel 2 controller on my JJ. The petrel 1 often after a dive shows a low battery, that suddenly jumps back up to full. Battery type is Saft. Even with new batteries it does this. Same happens to my buddies. Will this cap sort out this poor connection?

  5. Avatar Steven Forster

    I have an issue with my Petrel 1 resetting randomly, seems to be battery cap related.

    Is there a new battery cap that you can send to rectify this issue?

    • Shearwater Research Shearwater Research

      Hi Steven, If there are no good contacts the battery cap will only cover one side. You may need to send in your unit to the Service Centre. Shearwater will cover the repair. Our nearest repair centre from Australia will be our Asia/Pac Repair Center (Rob Edward) in Wellington, NZ. Their email address is and phone number is +64 21 535378. I will forward your email over to our Repair Centre and have them connect with you. Should you have any other additional questions, please don’t hesitate to email us at Thank you.

    • Shearwater Research Shearwater Research

      Hi, Steven. Sorry to hear you are having problems. Please send us an email to Make sure you include your physical address along with your request so that we can send you the battery cap you need.


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