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Tools and Products You'll Need
Recommended Products
| Product | What it's for | Key published spec | Link |
|---|---|---|---|
| PULADU Original MT1620 for Light Energy Solar Energy Sports Watch Battery Pa NAS. onic | Replacement rechargeable cell for solar movements that take an MT1620 | Listed as an MT1620 for light energy / solar energy sports watch battery [S3] | Check Price on Amazon |
| Citizen Q&Q Analog Solar Watch, 10 ATM Water-Resistant, Nylon Strap, navy, Classic | A simple solar analog to replace an ageing watch outright | Approximately 3.5 months of operation with a full charge; 10 ATM water resistance; approx. 37 mm diameter [S4] | Check Price on Amazon |
| Garmin Enduro 2 – Ultraperformance Watch, Long-Lasting GPS Battery Life, Solar Charging, Preloaded Maps (Renewed) | Solar-assisted GPS sports watch where sun extends, not replaces, charging | Power Sapphire lens harvests solar energy for more time between charges; AutoSelect/SatIQ manages GPS power draw [S5] | Check Price on Amazon |
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Last Updated: September 2026
- A wristwatch brand developed by the Japanese watch manufacturer Citizen
- Photovoltaic Power: Generates electricity from light and continues to operate by charging, eliminating the need for regular battery replacement
- The 1.4” Power Sapphire lens harvests the sun’s energy, giving you more power and time between charges
- AutoSelect mode uses SatIQ technology to dynamically determine the GPS mode necessary to maximize battery life without compromising positional accuracy
The Short Answer
A solar watch does not run on a disposable battery. It runs on a rechargeable secondary cell (older models used a capacitor) that the dial's photovoltaic layer keeps topped up. That cell is a consumable part with a finite number of charge cycles, so it degrades gradually over years rather than dying suddenly like a coin cell.
The practical signal is not age, it is reserve. When a fully charged watch stops holding its rated power reserve, the cell is wearing out. Citizen's Q&Q solar listing, for example, states approximately 3.5 months of operation from a full charge [S4]. If a watch with that kind of published reserve starts stopping after a long weekend in a drawer, the cell is the suspect — not the solar panel.
The Problem: "My Solar Watch Holds a Charge for Less Time"
Here's the thing about how these movements fail. They rarely announce it. The watch keeps running perfectly while you wear it in daylight, because the panel is feeding it every day. The wear only shows up in the gap — the overnight, the week in a drawer, the winter of long sleeves.
Common symptoms that point at the storage cell rather than at the light source:
- The watch runs fine on the wrist but dies within days off the wrist.
- It reaches full charge quickly, then drains far faster than the published reserve.
- The second hand starts moving in two-second jumps (a low-charge warning behaviour on many solar analog movements) even after long light exposure.
- Recharging no longer clears the low-power warning at all.
Step-by-Step: Diagnose Before You Replace
Step 1 — Force a full charge. Put the watch face-up in indirect daylight, not behind window glass in direct summer sun, and leave it for a full day or more. Direct, prolonged sun heats a watch case; heat is unkind to any rechargeable chemistry.
Step 2 — Note the start point. Once the low-power warning clears and the watch keeps normal time, write down the date.
Step 3 — Store it in the dark. Drawer, box, sleeve. No light at all.
Step 4 — Check daily and record the day it stops. That number is your real reserve.
Step 5 — Compare against the model's published reserve. For the Citizen Q&Q model above, the listing figure to compare against is approximately 3.5 months from a full charge [S4]. If you are getting a small fraction of the manufacturer's published figure, the cell has lost capacity.
Step 6 — Decide: service, self-replace, or replace the watch. More on that below.
PULADU Original MT1620 for Light Energy Solar Energy Sports Watch Battery Pa NAS. onic — Best for a like-for-like MT1620 cell swap
The supplied listing identifies this as an MT1620 cell for light energy / solar energy sports watches [S3]. That is the whole of the published specification here, and it matters: MT1620 is a specific cell designation, so this is only the right part if your movement's service documentation calls for an MT1620. Nothing in the supplied listing information states a capacity in mAh, a cycle rating, a warranty, or a compatibility list of watch calibres.
So treat it as a part number match, not a universal fix. Open your caseback only if you have the tools, a gasket you are willing to replace, and no water-resistance rating you care about preserving — and note that opening a case yourself typically ends any factory water-resistance guarantee.
Suits: someone whose watchmaker or service manual has already named MT1620 as the correct cell.
Limitation: the supplied listing does not state capacity, cycle life, or which watch models it fits.
Citizen Q&Q Analog Solar Watch — Best for replacing a tired solar analog with a published charge reserve
This one earns its slot on one number: the listing states approximately 3.5 months of operation with a full charge [S4], which gives you an actual benchmark to measure a future decline against. That is more than most solar listings tell you. The same record lists photovoltaic power that keeps the watch running by charging rather than requiring regular battery replacement, 10 ATM water resistance, an approximately 37 mm diameter unisex case, a nylon strap, and a Japanese movement [S4].
At roughly 37 mm this is a small-to-mid-size case by modern standards, which reads as a compact everyday watch rather than a wrist-filling sports piece [S4]. The listing also notes the manual's English language is not guaranteed and that the country of origin is China [S4].
Suits: a reader whose old solar watch has lost its reserve and who wants a plain, legible, water-resistant daily wearer with a stated reserve figure.
Limitation: documentation may not arrive in English, per the listing [S4].
Garmin Enduro 2 – Ultraperformance Watch — Best for solar as a range extender on a GPS watch
Important distinction, and people get this wrong constantly: solar on a GPS sports watch is supplemental. Garmin's listing describes the 1.4-inch Power Sapphire lens as harvesting the sun's energy to give more power and time between charges [S5]. "Between charges" is the operative phrase — you still plug it in.
The listing also describes AutoSelect mode using SatIQ technology to pick the GPS mode needed without compromising positional accuracy, preloaded TopoActive and ski maps, an UltraFit nylon band, NextFork intersection distances, grade-adjusted pace, and an LED flashlight the listing describes as twice as bright as the fēnix 7X [S5]. Note this specific record is a Renewed unit.
Suits: trail and ultra runners who want sunlight to stretch a charge on long days out.
Limitation: it is a rechargeable-by-cable device, so solar reduces charging frequency rather than eliminating it [S5].
Tips for Best Results
- Give the watch daylight regularly instead of rescuing it from empty. Deep, repeated discharges are hard on rechargeable chemistry.
- Rotate a collection. A solar watch left in a dark box for months is being run to flat over and over.
- Avoid baking it. Indirect daylight on a windowsill in shade, not a car dashboard in July.
- Watch the seconds hand. Two-second stepping is a designed low-power warning on many solar analogs — respond to it.
- Log the reserve once a year. A single dated number per year turns a vague feeling into evidence.
Common Mistakes to Avoid
- Asking a jeweller for "a new battery." Solar movements need the correct rechargeable cell; a standard coin cell is not a substitute.
- Opening a water-resistant case at the kitchen table. The Citizen Q&Q listing's 10 ATM rating [S4] depends on intact gaskets and a properly closed caseback.
- Buying a cell by size alone. The PULADU part is published as an MT1620 [S3]; confirm your movement calls for that designation.
- Blaming the cell when the real issue is lifestyle. Long sleeves plus an indoor desk job starves the panel.
- Assuming solar means never charging. The Citizen Q&Q Analog Solar Watch, 10 ATM Water-Resistant, Nylon Strap, navy, Classic listing states that photovoltaic power generates electricity from light and keeps the watch running by charging, eliminating the need for regular battery replacement, and that a full charge gives approximately 3.5 months of operation — so it still depends on light [S4]. On a GPS watch like the Enduro 2, solar extends time between charges [S5].
How We Research
This website does not perform hands-on testing. For this guide, product facts were drawn from Amazon Creators API verified product records and the product listing feature bullets for each ASIN, retrieved 2026-09-09, then read closely and compared against one another. Where a listing does not state something — capacity, cycle life, warranty term — this article says so instead of estimating. General consumer-safety context is available from the CPSC [S1] and USA.gov's consumer protection resources [S2].
Final Verdict
If your solar watch still runs on the wrist but dies in a drawer, the rechargeable cell is aging — that is the diagnosis, and it is normal. Do the dark-storage test first, because a measured reserve beats a guess.
For a documented DIY-path part, the PULADU Original MT1620 for Light Energy Solar Energy Sports Watch Battery Pa NAS. onic is only worth buying once your movement's documentation names MT1620 [S3]. If you would rather start fresh with a simple, legible watch that publishes its reserve, the Citizen Q&Q Analog Solar Watch is the sensible pick precisely because its listing commits to approximately 3.5 months of operation from a full charge and 10 ATM water resistance [S4]. And if your real problem is running out of GPS on long days, the Garmin Enduro 2 is the different animal — its Power Sapphire lens is published as extending time between charges, not removing the cable [S5].
Related Resources
- How solar watch movements generate power
- Water resistance ratings explained
- Quartz vs mechanical vs solar: which to buy
Sources & Methodology
Nobody at this website took a caseback off, ran a discharge clock, or put a watch on a wrist — no physical or laboratory testing was done here, full stop. What was done: the Amazon Creators API verified product records and every supplied listing feature bullet for the three ASINs above were read line by line on 2026-09-09, and the published figures were compared to see which claims are specific (a stated 3.5-month reserve, a 10 ATM rating, an MT1620 designation) and which are marketing language. For solar watches, that level of reading is genuinely enough to tell you whether a listing commits to a charge reserve you can later measure your own watch against — which is the single most useful thing a spec sheet can give you in this category.