Correct Battery for Seamaster Ref 2511?

Hi folks,

I've just acquired a quartz Seamaster 120m (1992-ish) reference 2511.41 (originally for Japanese market). I assume the watch is identical to other ref 2511.xx except for the dial and handset.

The watch is currently running with a SR927SW (aka Renata 395) but my understanding is that the correct battery for that watch is a Renata 371. The physical dimensions of those two batteries are not identical. The 395 is a bit thicker, so if is incorrect, it could be putting extra pressure on the movement/movement cover.

By chance, does anyone know the correct replacement battery?

Thanks in advance,
Stephen

Caliber?

Omega 1438 (modified ETA 255.461)

But my understanding is that is primarily the watch case that determines the specific battery model. For example, the 370, 371, 372, 373, 380, 394, 395, 397, and 300 are all 9.5mm in diameter and would all work fine to power the bare movement. The difference between them is the height, and that varies to accomodate different case thickness. Or at least that's my understanding.

The battery compartment of a movement is designed for the caliber, not the case.

Here is a detailed explanation of the 1438/1538 battery sizes.

https://omegaforums.net/threads/what-battery-fro-omega-2264-50.73831/#post-994319

Thanks for that tip. It explains the discrepancy between 395 and 371. Though why battery manufacturers would change the dimensions of a battery model yet keep the same model number is beyond me. Since my watch doesn't have the added retaining clip for a 371, and since it runs fine with the 395, I think I can stick with that. From the linked comment it sounds like the worst case scenario for the using current version of the 395 is the battery does not stay in place under a mechanical shock.

Just to wrap this up, the case can determine the specific battery. Here's an excerpt from Omega Technical Guide TG-19-C-013-E: Note the admonition on page 4:

It's both actually. Thinner cases may take a thinner battery - using a thicker battery in a thinner case can cause damage to the movement.

I learn something new nearly every day.

It was a bit surprising to me as well. But it's more plausible when looking at the movement. On my 1438 (without the added retaining clip noted in the post above), there is a depression into which the battery is seated, but there is nothing on the movement itself that holds the battery in that depression or otherwise constrains the battery's thickness, i.e. its height above the movement. The battery simply sits in the depression. What keeps the battery in place is the internal cover that's matched to the case. The cover sits on top of the movement and presumably keeps the battery from moving vertically and thus escaping it's depression. So a different case could potentially change how far above the movement that cover is positioned, necessitating a thinner or thicker battery.

I must say that I'm still a little skeptical of Omega's explanation that battery manufacturers changed the shape of the 395 while keeping the same part number. It's not something one company alone could have done; it would have required a coordinated effort among all battery manufacturers. I wonder if the real explanation is that the original 1438's retaining mechanism (i.e. the internal cover) was always a little sketchy. Perhaps after enough service complaints Omega decided to fix the problem by adding a retaining clip. And the stated reason (battery changed shape!) is just a convenient excuse. With that addition, though, it's certainly true that a 395 battery plus the thickness of the clip would no longer fit in the case. So adding the clip required changing to a thinner battery. That's all speculation, though. I have no inside information from Omega and (despite degrees in Electrical Engineering 😀 ) no particular insight into consumer batteries.

No, all it takes is one, Renata. Renata is owned by the Swatch Group.

The portion of the technical document you post above is an old version. Now these only specify the Renata number, not any other manufacturer, for obvious reasons...

Nailed it!

I had originally installed a Renata 395 in the watch and was not impressed with how well it was retained in the movement's battery compartment. It just sort of lays loosely on top of the battery terminal. @Archer's comment got me curious enough to order a (supposedly equivalent) muRata SR927. They arrived today. I swapped out the Renata for the muRata, and the Japanese battery fits perfectly and securely in the movement. Both batteries are 9.5mm in diameter with an outer cylinder (positive terminal) 2.3mm in height. But critically, the negative terminal of the muRata protrudes slightly further than that of the Renata. The overall thickness of the muRata is 2.6mm; the Renata is 2.5mm.

So the answer to the question I originally posed appears to be:

- If your movement has the special retaining clip installed, use a Renata 371
- Otherwise use a muRata/Sony/etc. SR927/S/SW

The watch actually worked fine for the week that it had a Renata 395 installed, but the SR927 definitely fits the movement better.