Seiko Caliber 4M21 Watch Movement

Manufacturer	Seiko
Caliber Number	4M21, 4M21A
Movement Type	Kinetic (AGS), quartz
Lignes	11.5”’
Diameter	25.6mm
Height	2.7mm
Jewel Count	9
Frequency	32,768 Hz
Accuracy Rating	+/- 15 seconds/month
Capacitor	30274MZ, 302729R (discontinued ?)
Power Reserve	3-4 days on full charge
Energy Current	.60 uA movement, .20 uA circuit
Hand-Windable?	No
Driving System	Step motor
Hand Count	3
Functions	Central hours; central minutes; central seconds; power reserve indicator
Other Features	Low energy warning (EOL), instant-start function, overcharge prevention (cannot be overcharged)
Hacking Seconds?	Yes
Country of Manufacture	Made in Japan
Known Models	Seiko Dolce AGS, Seiko SLB002, Laurel (Ref: LHFMZ02) (Add your watch to the comments below…)

The Seiko caliber 4M21 (4M21A) is a kinetic quartz watch movement from the 1990s.

The technology behind the 4M21 was introduced by Seiko in January 1988. At the time, they called it AGS, which stands for Automatic Generating System. Today, it is known as Kinetic. The idea behind it was to solve for the environmental problem caused by having to replace batteries in millions of watches. The AGS system used a rechargeable battery, reducing the need to throw away batteries every year or two.

While Kinetic watches use fewer batteries, they still need replaced eventually, especially if they are not charged for a long period of time.

The 4M21 is an early Kinetic movement, which at the onset of the tech, was able to run continuously for 3~4 days on a full charge. As you will learn in the section below, advancements to capacitor storage appear to allow for a much longer runtime.

Power Reserve:

The 4M21 uses a rechargeable battery/capacitor to store energy it accumulates from the automatic winding system. When the original capacitor is fully charges, it will provide about 3 to 4 days of runtime for the watch. In Seiko’s own words:

“When the capacitor is fully charged, the watch will keep operating for a maximum of 3 to 4 days without recharging the capacitor.” -Official 4M21 manual, page 13

It appears by the year 2000, Seiko updated the capacitor part numbers and corresponding power reserve:

Seiko Part #	Battery Type #	Power Reserve
3029114	SL614	3 days
3029116	ES614	3 days
30274MZ	MT616	42 days

If you replaced your capacitor with the updated 30274MZ, please comment below with how much runtime you are experiencing on a full charge…

Low Battery Indicator:

If the seconds hand on your 4M21 powered watch is ticking at 2-second intervals, it means the energy is low in the capacitor. When the seconds hand starts jumping, it means the watch has about 3 hours of “juice” remaining. You will need to shake the watch side to side (swing the watch as Seiko says) to start charging the cell.

If you swing the watch thousands of times and wear it daily but the seconds hand still skips, it means you likely need to replace the capacitor.

How many swings does it take to reach full power?

A lot. With the new style capacitor, it takes about 12,000 swings to reach the full power reserve to power the watch for 42 days. This is probably why Seiko recommends wearing your watch for 8-10 hours per day to keep it going.