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.
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.