The Seiko caliber V157 (actually marked V157A) is found in some Seiko solar-powered watches, including the exclusive Street Series Solar Divers.
V157 VS V157A:
The movement in your timepiece may actually be signed with the caliber number V157A. As with most (if not all) Seiko movements, the trailing letter indicates the evolution or change-log of the movement, starting with A as the first release. Therefore, V157 is the same as V157A. As of this post, there is not a V157B, V157C, and so on.
V157 VS V158:
There is a similar Seiko caliber V158, with the main difference being that the V158 has a day/date window at 3:00, and the V157 only displays the date at 3:00.
Seiko claims that the caliber V157 will maintain accuracy of +/- 15 seconds per month at normal operating temperatures of about 5C to 35C (41F – 140F).
The caliber V157 is a solar powered watch with a manganese titanium-lithium rechargeable capacitor. It is not a normal battery. The number is MT920, or more specifically: 302324Y. Order one here
The chart below shows how long different lights sources can take to fully charge the cell in the V157. This ranges from 120 hours to 9 hours of constant light source. A full charge can last up to 10 months.
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Although there is an instruction manual for dive watches with caliber V157 or V158, there is also another instruction manual that combines the following calibers: V110, V111, V114, V115, V116, V137, V145, V147, V157, V158, V181, V182, and V187.