Notes on Changing Watch Batteries

Published: October 3, 2020

Over the years, we have received many watches for “battery changes” that were damaged because someone who didn’t know how to replace a battery attempted to replace a battery. Sadly, a few of these were damaged beyond repair. Changing a watch battery is not hard. Changing a watch battery with no damage to the case or watch movement, however, should be the domain of the qualified watchmaker for best results. Many people find out that the money they thought they were saving on a battery change is a fraction of what they end up spending to repair their now damaged watch.

On the Batteries Themselves

Quartz watches run on a “cell,” commonly called a “battery”. There are slow drain cells, fast drain cells, and multi-drain cells. Among a plethora of watch battery brands, we most commonly encounter Energizer, Murata, Maxwell, Panasonic, Renata, and Varta in watches. Recently, we discovered a battery branded “Union Carbide” in a watch that had been in a drawer for a couple of decades.

All of the modern battery brands deliver a largely equivalent performance in power delivery. The biggest improvement of the last decade has been the insulators between the positive and negative contacts less commonly leaking battery acid into the movement.

The biggest problem in the past decade has been a relaxing of quality control regarding the form factor (the dimensions) of batteries. Two years ago, we had major issues with ETA F03.111, F04.111, F05.111, F06.111, and F07.111 movements (we lovingly call these the “F Troop” or “F Series” movements). The F Series has been used in many luxury watches, and always came from the manufacturer with a Renata battery installed. However, many watch repair businesses have refused to use Renata batteries due to their reputation for leaking (this has not been an issue for a long time.

We found that we were getting many of these watches in after someone else had changed the battery with complaints that the watch was losing time. The reality is that if you install a Renata battery in these movements, they will work perfectly. Energizer batteries, loved by watchmakers and used without problem in every other movement we are aware of, are slightly larger than Renata batteries. In some instances, by as much as .15mm!

We have tested this scenario thoroughly and found that some F Series movements with an Energizer battery can show 15 minute a day losses (especially during the calendar change) with an Energizer battery and then keep perfect time with a Renata battery. The slightly larger Energizer battery causes a bind in the movement, which causes this loss in time.

For virtually every mother movement, battery manufacturer is inconsequential.

Handle with Care

If your watch isn’t handled with care, there are a lot of things that can be damaged.

The Watch Case

Watch cases are commonly damaged during the opening process. Friction fit cases can be seriously marred or scratched when someone inexperienced at opening them slips. In extreme cases, this can damage sealing surfaces, rendering a formerly waterproof watch not waterproof.

For cases with a screw down case back, fitment of the a proper jig ensures the case back is not damaged. Sadly, many use hand-held casing wrenches designed over fifty years ago to save time. These almost always leave some marring on the case back.

When reinstalling a watch case back, the threads should always be cleaned and a lubricant such as Fomblin applied. This protects the threading, and allows the case to be opened more reliably at the next intervention.

It is a good idea to perform a pressure test on water resistant watches when you change their battery, especially if your watch is valuable or meaningful to you. It is common for gaskets to fail and begin to leak at the crown and caseback, as well as around the crystal. Water leaking into your watch can damage the movement, calendar, dial, and hands. The best case scenario is that they can be replaced. In some instances where the watch is no longer supported, dials must be refinished. This avoidable scenario has caused much sadness to watch lovers over the years.

The Movement

The stories we could tell.” Seriously. People do some bad things to watch movements.

Watch Technicians with improper training do not know how to dress screwdrivers to fit the screws in each watch. When a screwdriver is not dressed to fit the screw, it is likely to slip and scratch the movement. Some of these slips cause aesthetic damage only, but this is not acceptable. Some slips cause actual functional damage. This is even less acceptable.

Coils are commonly scratched by screwdrivers that slip out of screwheads as they are turned. These are part of the Lavet motor that drives the gear train. When the coil is scratched, electrical insulation is lost and the watch is essentially shorted. This requires an expensive new coil or a completely new circuit.

In some “thinline” movements, a slipping screwdriver can be driven into the battery well, making contact with the back of the dial. This can cause irreparable damage to the dial. The best case is that your watch will look worse for the wear. If the screw driver hits hard enough to really dent the dial, the protrusion might be enough to block the movement of the hands. If the dial is made of natural material such as Mother of Pearl or stone, it could be cracked.

Untrained watch technicians have been known to put the battery in backwards. This will destroy some movements. Our watchmakers are careful to install the proper battery in your watch and to identify the correct orientation of batteries. You may laugh at this. And you’d be right to think that this is simple. Sadly, this exact issue causes a lot of damage to watches, and we fix a lot of bad work other people do.

All Work Should be Tested

Any watchmaker or watch technician worth their salt will test the water resistance of each watch they change the battery on (if water resistant) and check the performance of the movement. We perform a dry test at minimum on each water resistant watch we change the batteries of. Luxury watches normally receive a vacuum test, a pressure test, and a condensation.

If your watch is not water resistant, we will quote you on repairing the issue. On luxury watches, we recommend changing the gaskets at each service. Gaskets get brittle, crack, and deteriorate with age and exposure. Just because a watch passes a test now doesn’t mean your ten year old gaskets will be good a year from now. Proactively replacing gaskets protects your investment.

It is befuddling to think about the number of watch repair companies who change batteries in watches and then don’t test the performance of the movement. What is the point of putting a battery in a watch, making sure it is water resistant, and giving it back to the customer only for them to notice in a few days that the watch is losing time? There is no point.

We test the performance of the movement in every quartz watch we work on, whether it is getting a new battery or a full service. At a minimum, we test the consumption, the lower working voltage, and the acoustic rate of the movement. We use a Witschi Q Test 6000 or a Witschi Analyzer Q1 for this work.

The Bottom Line

Someone competent needs to change the battery in your watch, and we would love to be the company to serve you. Whether your watch needs a battery, or a repair from a battery change gone bad, We Fix Watches can help you. Contact us today for a quote here.