About this replacement
Insignia Flex 8" NS-15AT08 — 3.7V Li-Polymer Replacement Battery (PR-3956155)
This 3.7V, 4000mAh lithium-polymer battery replaces part number PR-3956155 in the Insignia Flex 8" tablet (NS-15AT08). It fits the 8-inch Android tablet and restores power to the display, processor, and wireless radios. Voltage and physical dimensions match the original cell exactly at 155.90 × 56.35 × 3.70mm.
- Flex 8" and NS-15AT08 compatibility: Both model references point to the same hardware generation. They share the same connector pinout, voltage rail, and charge IC handshake — so one cell covers both SKUs without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the NS-15AT08 board. The BMS accepted the new cell without fault flags, and the charge IC negotiated current correctly from the first cycle.
- Fuel gauge reset after installation: After fitting this battery, run the tablet down to automatic shutoff, then charge uninterrupted to 100% before using it. This one full cycle recalibrates the fuel gauge IC against the new cell and corrects the inaccurate percentage readings that appear immediately after a swap.
Tablet shutting down at 15–25% remaining after battery swap
This happens when the fuel gauge IC is still calibrated to the old cell's voltage curve. The tablet's power manager reads the new cell's voltage and maps it against the wrong reference — it interprets a still-usable voltage level as critically low and forces shutdown. The combined load of the display at full brightness plus active WiFi pulls enough current to cause a brief voltage dip, which triggers the cutoff early. Run one full discharge to automatic shutoff, then charge to 100% without interruption — after that cycle the shutdowns at 20-25% stop.
Fast charging not available after fitting the PR-3956155
The Insignia Flex 8" uses a USB charge negotiation step that must complete at least one accepted cycle before the charge IC locks in the higher current profile. If the tablet only shows slow charging after installation, that is expected on the first charge. Plug into the original wall adapter — not a PC USB port — and let it charge fully without interruption. After that first complete cycle, the charge IC recognises the new cell and the standard charge rate resumes.