PRS18Q-COSC battery change

[bambam]

My PRS18Q-COSC is indicating battery end of life - second hand stuttering - does anyone know what battery it needs?

First battery change since buying it new in 2018 so anything to look out for when replacing? Or is straight forward?

Cheers

[walkerwek1958]

FO6.411 movement, takes a 371 battery. Take great care not to touch the coil with anything metallic!

[TaketheCannoli]

Use a toothpick to lift the battery out. As Paul says, don't use anything metal.

[bambam]

FO6.411 movement, takes a 371 battery. Take great care not to touch the coil with anything metallic!

Use a toothpick to lift the battery out. As Paul says, don't use anything metal.

Thanks chaps! Advice noted re using metallic objects.
Any advice or things to look out for when re-sealing?

[prexelor]

FO6.411 movement, takes a 371 battery. Take great care not to touch the coil with anything metallic!

I know nothing about how watches work. What would happen if something metallic was used?

[TaketheCannoli]

If, and it is an if, you were to touch the coil you’d be likely to kill the movement.

I know nothing about how watches work. What would happen if something metallic was used?

[walkerwek1958]

Just be sure that the O ring has located correctly, if you're careful it will remain in the groove where it should be. If it does come free be careful to refit it and check as you screw the caseback that it hasn`t come free. As ever, good lighting and a magnifier are essential.

Another point to remember: clean the area around the caseback seal before removing the caseback, this will safeguard against debris getting into the watch, it only takes a spec of dirt on the train wheels to stop a quartz movement.

There's a simple trick to minimise the risk of marking the caseback when removing. Stick a strip of insulating tape over the caseback notches, then mark them with a marker pen. When the removing tool is located there's far less chance of marking the back with it. When twisting apply more clamping pressure as turning pressure, this should safeguard against the tool slipping if its adjusted properly. Once its moving use a sticky ball. Likewise with replacement, use the sticky ball to get it as tight as possible then nip it up a touch with a Jaxa or similar, if the seal is correctly located there is nothing to be gained by over-tightening.

[TaketheCannoli]

Ideally you’d remove the caseback gasket and coat it in silicone grease before replacing but if you’re not going to do that then unscrew the back and lift it off carefully, trying not to dislodge the gasket. You’ll be able to see it, it’s a fine black rubber ring.

Lift the battery out with a toothpick and drop the new one in the same way. Replace and screw down the back. All should be well in a three year old watch.

Thanks chaps! Advice noted re using metallic objects.
Any advice or things to look out for when re-sealing?

[TheTigerUK]

When changing a battery after a couple of years in a watch I always replace the case back gasket, false economy to reuse (IMO) I also use a fine Sharpie to write the date on the battery, 8/21 for today.

[walkerwek1958]

Caseback gaskets need only a fine trace of silicone grease applying, the purpose is to reduce friction as the caseback is tightened thus avoiding the gasket being pulled out of position. Once a gasket has been treated it shouldn’t need treating again, the silicone grease will become bonded to the surface. Excess grease just makes a mess and if the gasket gets displaced or dropped during handling there’s risk it’ll smear onto the movement.

Replacing a gasket is fine if there’s doubts about condition, but finding the correct size can be a challenge. I have a large stock of O rings in different thicknesses so I’m confident I can replace virtually anything, but getting the thickness correct is still tricky. I measure the old one at its narrowest and thickest points using a digital caliper and take the average, but this often gives an imprecise result because O rings aren’t easy to measure, so a degree of judgement is needed. I sometimes end up trying different thicknesses and deciding which is better, as the caseback screws down its possible to feel the friction as it contacts the seal and compresses it. If all’s well the caseback will turn further before becoming tight as it contacts the case. If the gasket is too thick it won't be possible to compress it sufficiently to get the caseback to make metal to metal contact and the force required to tighten will increase more gradually, this isn’t an ideal situation because the caseback isn’t fully home, although the watch will probably be sealed from water ingress.

If the gasket fitted is in good condition and still performing its function there’s a good argument for keeping it unless you can be certain you can find the correct replacement, replacing it with one that doesn’t fit properly will do more harm than good. Modern neoprene rubber doesn’t degrade like the older stuff but its worth giving it a prod with a blunt cocktail stick or similar to check it’s still supple and has sufficient elasticity.

[number2]

Caseback gaskets need only a fine trace of silicone grease applying, the purpose is to reduce friction as the caseback is tightened thus avoiding the gasket being pulled out of position. Once a gasket has been treated it shouldn’t need treating again, the silicone grease will become bonded to the surface. Excess grease just makes a mess and if the gasket gets displaced or dropped during handling there’s risk it’ll smear onto the movement.

Replacing a gasket is fine if there’s doubts about condition, but finding the correct size can be a challenge. I have a large stock of O rings in different thicknesses so I’m confident I can replace virtually anything, but getting the thickness correct is still tricky. I measure the old one at its narrowest and thickest points using a digital caliper and take the average, but this often gives an imprecise result because O rings aren’t easy to measure, so a degree of judgement is needed. I sometimes end up trying different thicknesses and deciding which is better, as the caseback screws down its possible to feel the friction as it contacts the seal and compresses it. If all’s well the caseback will turn further before becoming tight as it contacts the case. If the gasket is too thick it won't be possible to compress it sufficiently to get the caseback to make metal to metal contact and the force required to tighten will increase more gradually, this isn’t an ideal situation because the caseback isn’t fully home, although the watch will probably be sealed from water ingress.

If the gasket fitted is in good condition and still performing its function there’s a good argument for keeping it unless you can be certain you can find the correct replacement, replacing it with one that doesn’t fit properly will do more harm than good. Modern neoprene rubber doesn’t degrade like the older stuff but its worth giving it a prod with a blunt cocktail stick or similar to check it’s still supple and has sufficient elasticity.

You're a goldmine of information Paul

[TheTigerUK]

Caseback gaskets need only a fine trace of silicone grease applying, the purpose is to reduce friction as the caseback is tightened thus avoiding the gasket being pulled out of position. Once a gasket has been treated it shouldn’t need treating again, the silicone grease will become bonded to the surface. Excess grease just makes a mess and if the gasket gets displaced or dropped during handling there’s risk it’ll smear onto the movement.

Replacing a gasket is fine if there’s doubts about condition, but finding the correct size can be a challenge. I have a large stock of O rings in different thicknesses so I’m confident I can replace virtually anything, but getting the thickness correct is still tricky. I measure the old one at its narrowest and thickest points using a digital caliper and take the average, but this often gives an imprecise result because O rings aren’t easy to measure, so a degree of judgement is needed. I sometimes end up trying different thicknesses and deciding which is better, as the caseback screws down its possible to feel the friction as it contacts the seal and compresses it. If all’s well the caseback will turn further before becoming tight as it contacts the case. If the gasket is too thick it won't be possible to compress it sufficiently to get the caseback to make metal to metal contact and the force required to tighten will increase more gradually, this isn’t an ideal situation because the caseback isn’t fully home, although the watch will probably be sealed from water ingress.

If the gasket fitted is in good condition and still performing its function there’s a good argument for keeping it unless you can be certain you can find the correct replacement, replacing it with one that doesn’t fit properly will do more harm than good. Modern neoprene rubber doesn’t degrade like the older stuff but its worth giving it a prod with a blunt cocktail stick or similar to check it’s still supple and has sufficient elasticity.

Because I only change the gaskets in a small range of Seiko's I always have the correct OEM gasket to use or a suitable generic, I find old/used ones often go hard, brittle and out of shape and really do need replacing.

[bambam]

@walkerwek1958 - that is really helpful, thanks.
I’ll do my best to follow your guidance. Will probably use a toothpick or small wooden stirrer to apply the silicon to the gasket.

Battery ordered and silicon lubricant on stand-by.