For expensive or antique watches we can only emphasize in the strongest terms that changing the battery should only be carried by a professional jeweller or specialist. In some cases (Rolex, Omega etc) only their authorized dealers should be used.
The vast majority of watch backs simply click into place. Some however require the use of specialist watch back compressor. These are readily available on the internet and are relatively cheap. To avoid having to use one do not apply too much force in removing the back off as this is an indication that one will be required when you come to put the back on again.
The two main types of back are the non-waterproof and waterproof. Many batteries can be removed without the need of specialist jewellery tools.
These are usually easily removed by inserting a blunted knife along the rim of the back. Flip upwards and the back should pop off. For some the back has a rubber ring around its interior rim. This ring ought to be renewed however so long as you are careful and it is not damaged you can replace the original rubber ring.
These will have to be rotated in an anticlockwise motion to unscrew them from the body of the watch. There are specialist tools for doing this with a range of inexpensive adjustable removing tools. It is best not to attempt it without one of these tools as it is essential they are screwed back on to the same torque in order to preserve their waterproof seal.
Most of our watches use the most common battery which is a 377. (sometimes identified by its alternative number 626 sw). There are nevertheless a large range of batteries which vary in size and voltage. The battery can usually be identified by its number on the top side of the battery. Please always ensure you have the right battery as sometimes the same sized battery can be of completely different voltage and amps output. The top of the battery is marked with either a + (positive) or a - (negative).
This depends on whether the battery is screwed into its base or is merely held in place by a clip around it. If its the later then you can gently place the edge of a small flat screwdriver underneath it and gently flip it up and out. If it is retained by screws you will have to unscrew them taking care to remember their corresponding location.
Insertion is a straightforward reversal of the removal operation. Care should be exercised to replace the battery with the same side facing upwards. (98% of watches have the + side facing upwards). Also try and use a pair of non metal tweezers. The image shows the use of a plastic clothes peg holding the battery over the bay in which it sits. You can then press down with a plastic pen or similar non metal object.
Before you begin the operation you should either wear an earthling strap or hold a metal bar to discharge the static electricity that builds in your hand. One milliamp of static electricity is enough to short circuit a mechanism. Ideally wear disposable rubber gloves.
Is it worth it? Most low end watches are made with their early disposal in mind. In other words they are not expected to last beyond the lifetime of the battery. Therefore if the watch you are thinking on replacing a battery costs less than £5 to replace, consideration must be given as to whether the time you spend on it is actually viable.
If you are required to remove screws carry out the operation over some sort of tray lined with a sheet of white paper so that you can easily find the screws and battery. It is not recommended to use a magnetic screwdriver as this can magnetize the watch.
Care should be taken to dispose the old battery properly. Never leave them in a room with children as some contain mercury, lithium and various other highly toxic chemicals.
Sometimes you may find that the second hand repeatedly moves backwards and forwards. This is sign that the watch has become magnetized. In other words the minute hand has become magnetic and is pulling the second hand anti-clockwise. To de-magnetize you can use a cheap tool called a de-magnister by simply placing the watch over its inner electro magnet.