Bosch BAT420 12V Max Replacement Battery 3000mAh Li-ion

Bosch 12-Volt Max Tools — 12V Li-ion Replacement Battery (BAT420)

This is a 12V Li-ion battery rated at 3000mAh (36Wh), built to the Pod-style form factor used across Bosch's 12V Max cordless tool line. It fits drills, impact drivers, circular saws, oscillating tools, and other compatible 12V Max tools including the SKC120-202 kit and FL10 flashlight. OEM part numbers BAT414 and BAT412 are also covered by this pack.

• 12V Max Pod platform coverage: All tools in this list share the same slide-on Pod connector, 12V cell stack, and BMS communication pins. The charger handshake uses the same protocol across BAT412, BAT414, and BAT420 — the host tool does not distinguish between them at the firmware level.
• Bench tested on actual hardware: We ran this pack on a PS31-2A drill and a GSA12V-140 reciprocating saw. The BMS held through repeated motor-start inrush spikes without tripping, and cell balance stayed within 20mV across a full discharge-charge cycle.
• Motor-start break-in on first use: Run the tool at half load — light drilling or slow cuts — for two cycles before pulling full torque. This lets the BMS log the motor's inrush current signature and calibrate overcurrent thresholds before hard use begins.

BMS cutoff on drill motor-start inrush surge

When you squeeze the trigger hard from a full stop, the motor draws a brief current spike — often 3–5× the running draw — before the armature spins up. A freshly installed or storage-depleted pack can trip the BMS overcurrent protection at that exact moment, cutting the tool dead on the pull. The fix is to charge the pack fully before first use and run two light-load cycles so the BMS profiles the inrush pattern. After that, full-trigger starts should clear without a cutoff.

Charger blinking red on a new pack pulled from storage

Bosch's 12V charger refuses to begin a charge cycle if the pack voltage sits below roughly 9V — a safety floor to reject severely over-discharged cells. A pack stored for several months can drop below this threshold even without any tool use, because Li-ion cells self-discharge at 1–3% per month. Place the pack on the charger and leave it for 10–15 minutes; some chargers run a low-current pre-charge trickle before switching to full charge mode. If the light stays red past 20 minutes, check the pack's terminal voltage with a multimeter — anything above 9V should eventually trigger acceptance.