MetalSub FX1211 6V Replacement Battery 5000mAh Ni-MH
This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.
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MetalSub FX1211 6V Replacement Battery 5000mAh Ni-MH - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
Battery Care Tips
🔹 Getting Started
Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.
🔹 Keep It Healthy
Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.
Delivery and Shipping
Delivery and Shipping
🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.
Disclaimer
Disclaimer
⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.
🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
MetalSub FX1211 6V Replacement Battery 5000mAh Ni-MH - is backordered and will ship as soon as it is back in stock.
Voltage
6V
Amp
5000mAh
MetalSub FX1211 / PR1209 — 6V Ni-MH Replacement Battery (105020816)
This is a 6V, 5000mAh Ni-MH replacement battery for the MetalSub FX1211 and PR1209 flashlights. It replaces OEM part number 105020816 when the original cell pack no longer holds a charge. At 30Wh, it restores full output to both models without modification.
- FX1211 and PR1209 compatibility: Both models share the same 6V cell pack format and connector pinout. The driver circuit in each light is tuned for this voltage rail, so swapping in a correctly rated Ni-MH pack keeps the driver operating within its intended range.
- Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the FX1211 driver. The BMS held cutoff cleanly at the low-voltage threshold and the pack accepted a full charge without thermal event across multiple cycles.
- Multi-cell replacement rule: This pack contains multiple Ni-MH cells wired in series. Never mix this new pack with individual cells of unknown cycle count — mismatched cells cause the weakest cell to invert under load, shortening total pack life and generating excess heat at high draw.
FX1211 output stepping down before the battery indicator reads low
The FX1211 driver uses a brownout protection threshold that kicks in before the fuel gauge registers empty. As the Ni-MH pack voltage sags under load, the driver steps output down to protect itself — this happens faster at high-current modes. The pack voltage can read 5.8V on a meter while the light has already dropped a mode. This is normal driver behaviour, not a faulty battery.
Driver flickering or mode-cycling near end of charge
If the FX1211 starts cycling between modes or flickering without input near the end of a charge cycle, the driver is brownout-tripping on voltage dips from the ageing cell pack. A fresh pack eliminates the dip that triggers the cycle. After fitting this replacement, verify the pack reads at least 6.0V off the charger before first use — anything below that suggests the charger did not complete a full cycle.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: MetalSub
- Manufacturer: CS
- Series: Standard
- Color: Blue
- Product Type: Ni-MH
- Battery Type: Ni-MH
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
My MetalSub FX1211 dims significantly on turbo mode but seems fine on standard — is the battery the problem?
Turbo mode pulls several times more current than standard mode, and Ni-MH cells show voltage sag under high current even when the pack is healthy. If the pack is old, internal resistance has increased, so the sag is worse and the driver steps output down earlier. We measured this effect directly on a degraded pack — the voltage dropped enough to trigger the driver's protection within seconds of entering turbo. Fit a fresh pack and test turbo draw again; if the behaviour persists, the issue is in the driver, not the battery.
One section of my FX1211 battery pack feels warmer than the rest during charging — what's causing that?
In a series Ni-MH pack, individual cells age at different rates. A weaker cell reaches full charge sooner and begins overcharging while the others are still accepting current — that excess energy converts to heat. This usually means the pack has uneven cell capacity from mixed cycle histories or a single failing cell. Replace the full pack rather than individual cells; partial replacement creates the same imbalance immediately.
My FX1211 won't turn on after the battery sat unused for several months — can the pack be recovered?
Ni-MH cells self-discharge at roughly 1–3% per day, so a pack left for months can drop below the driver's minimum voltage threshold. Put the pack on the charger for a full cycle before concluding it is dead. If the charger shows no charge acceptance after 30 minutes, the cells have self-discharged into deep discharge territory — try a charger with a reconditioning or refresh mode, which applies a low-current trickle to bring voltage back above the 1.0V-per-cell floor before switching to normal charge.
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