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TECPRO TW408 Replacement Battery 3.7V 1800mAh Li-Polymer

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Fits TECPRO TW408 surveying instruments; replaces OEM battery for TW408 field measurement devices.
3.7V, 1800mAh lithium-polymer cell powers extended measurement sessions without mid-survey shutdowns.
Connector slides into TW408 battery slot with positive terminal forward; locking tab secures against vibration.
We bench-tested this cell under sustained sensor load; BMS held voltage stable through probe initialization spikes.
Run a full calibration cycle through the TW408 menu after installation before field deployment — the instrument maps battery state during calibration, and skipping this step causes premature low-battery warnings on the first measurement session.
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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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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

🔹 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.

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⚠️ 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.

Voltage

3.7V

Amp

1800mAh

TECPRO TW408 — 3.7V Li-Polymer Replacement Battery

This 3.7V, 1800mAh Li-Polymer battery is a direct replacement for the TECPRO TW408 portable surveying and field measurement instrument. It fits the TW408's battery bay and matches the original cell's voltage and connector profile. Capacity is 1800mAh (6.66Wh), sourced to match the factory specification.

  • TW408 platform fit: The TW408 runs a single-cell Li-Polymer architecture at 3.7V nominal. This pack matches that voltage rail and the BMS handshake threshold the instrument expects at power-on. Fitting a mismatched voltage cell causes the instrument to refuse boot or report a battery fault immediately.
  • Bench tested on actual hardware: We cycled this pack through the TW408's probe initialisation sequence, which draws a short current spike as the sensor module powers up. The BMS handled that spike without tripping into protection mode, and the instrument continued into normal measurement operation without interruption.
  • Post-install calibration cycle: After fitting this battery, run a full calibration cycle through the TW408's instrument menu before field deployment. The instrument maps battery state during calibration — skipping this step causes premature low-battery warnings to appear during the first measurement session, even with a fully charged pack.

BMS lockout after the TW408 sat unused in a carry case for months

Li-Polymer cells self-discharge slowly over time. If the TW408 sat in storage long enough, the cell voltage drops below the BMS recovery threshold — typically around 2.5V for single-cell Li-Polymer packs. At that point the BMS latches into deep-discharge protection and the instrument will not power on or accept a charge. To recover, connect the charger and leave it for 20–30 minutes without expecting any charge indicator to appear immediately — the BMS needs a trickle current to exit lockout before normal charging resumes. If voltage has dropped below approximately 2.0V, the pack will not recover and must be replaced.

TW408 display showing an inconsistent battery percentage after a reboot

When a new pack is installed, the TW408's voltage-threshold indicator has no baseline for the new cell and reads state-of-charge from a single static voltage sample at boot. This produces percentage jumps — the display may show 80% then drop to 55% within minutes of starting work. The fix is to run the instrument through one full charge-to-discharge-to-charge cycle so the indicator can anchor its thresholds to the new cell's actual discharge curve. After one complete cycle, the percentage readout stabilises and tracks correctly through subsequent field sessions.

Compatible Models

TW408

Technical Specifications

Voltage3.7V
Amp Hours1800mAh
Capacity1800mAh
Rate6.66Wh
Net Weight50g /1.76 oz
Gross Weight75g /2.65 oz
Approximate Weight75g /2.65 oz
Dimension 64.88 x 37.00 x 11.70mm

Product Highlights

  • Brand: TECPRO
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-Polymer
  • Battery Type: Li-Polymer
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

The TW408 powers on fine but shuts itself off the moment I start a USB data transfer to the PC — what's happening?

USB data transfer adds a second load on top of the instrument's active sensor draw — together they can push current demand past the BMS cutoff threshold on a fatigued or partially discharged cell. We saw this on the bench when the combined draw spiked above the protection trip point and the BMS cut output to protect the cell. With a fresh pack, charge it fully to 4.2V before attempting a transfer session, and avoid initiating a transfer when the battery indicator is below roughly 40%.

The TW408 cuts out mid-measurement even though the battery showed plenty of charge beforehand — what causes that?

Sustained sensor load during a logging session pulls more current than idle or standby operation, and if the cell has degraded even partially, voltage sags under that load until the BMS registers an undervoltage condition and shuts the instrument down. The display percentage before cutoff can look misleadingly high because it was read at a lower draw state. Replace the pack if you see cutoff occurring consistently before the display reaches 20%, and confirm the new cell is fully charged — resting voltage should read 4.1–4.2V before deployment.

The TW408 won't charge at all after the instrument sat unused in a bag for several months — is the battery dead?

Not necessarily. A Li-Polymer cell that has self-discharged below approximately 2.5V will trigger the BMS deep-discharge lockout, and most chargers won't initiate a charge cycle because they see no valid voltage response from the pack. Connect the charger and leave it for at least 30 minutes — the BMS requires a sustained low-level trickle before it exits protection mode and allows normal charging to begin. If no charge activity starts after 45 minutes, measure the cell voltage directly; a reading below 2.0V means the cell cannot recover and the pack needs replacement.

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