Quick answer
- Red + yellow fast blink on a DCB115 = pack fault. The charger refuses to charge because the battery's Battery Management System (BMS) is reporting a problem.
- Test another known-good battery first — if the second pack charges normally, the original pack is bad.
- Test the suspect pack on another DeWalt charger — if it faults on both, the battery is bad.
- If every battery faults on one charger, the charger is bad — DCB115 chargers occasionally develop an internal thermistor fault after ~3 years.
What the LEDs actually mean on a DCB115
DeWalt's DCB115 uses a simple two-color LED with three states:
- Slow red blink (≈1 per second): charging normally. Takes 30–90 minutes depending on pack capacity.
- Solid red: charging complete.
- Fast red blink + yellow (red/yellow alternating rapidly): pack fault. The charger has aborted the charge cycle because the BMS reported one of: cell imbalance, over-temperature, under-temperature, open cell, or failed handshake.
The red+yellow pattern does not automatically mean the battery is dead. It means the charger and battery failed to agree on whether to start charging. That can be a battery problem, a charger problem, or an environmental problem.
Quick checks before you replace anything
- Is the pack too cold or too hot? Lithium-ion refuses to charge below ~32°F (0°C) or above ~113°F (45°C). If the pack is cold from a truck bed or hot from heavy use, let it sit indoors for 30 minutes and try again.
- Inspect the pack contacts. Corrosion or debris on the pack rails will cause intermittent handshake failures. Wipe with isopropyl alcohol on a clean cloth.
- Inspect the charger bay. The small flexible contacts inside can bend over time — look for obviously bent or misaligned pins.
- Reseat the pack. Pull it out, blow out the bay, and press the pack in firmly until it clicks. A loose pack causes the same fault.
Step-by-step fix
-
Remove the pack and let it rest. If the pack was just used hard, wait 30+ minutes before re-inserting. Re-inserting a hot pack is the #1 cause of "fake" fault lights.
-
Clean the pack rails and charger bay. Isopropyl alcohol and a clean microfiber cloth. Do not use WD-40 or contact cleaner with oil residue — they attract dust and cause future handshake failures.
-
Swap in a known-good battery. If you have another DeWalt 20V MAX battery (any capacity, any age — DCB203 / DCB204 / DCB205 / DCB206 / FLEXVOLT DCB606, DCB609), put it on the suspect DCB115.
- If the second battery charges fine, the original pack is bad.
- If the second battery also faults, the charger is bad.
-
Swap in a known-good charger. If you have another DeWalt charger (DCB115, DCB118, DCB112), put the suspect pack on it.
- If the pack charges fine on the second charger, your DCB115 is bad.
- If the pack faults on both chargers, the pack is bad.
-
Check for swelling. A puffy, warped, or punctured pack is never safe. Stop using it, store it in a metal container outside your house, and take it to a Home Depot or Lowe's battery recycling bin.
-
Try a warm-up cycle (cold pack only). If the pack was in a cold garage or truck, bring it inside at room temperature for an hour, then re-attempt charging.
If it still isn't working
- Pack is under 2 years old and DeWalt-branded: it's likely still under the 3-year limited warranty. Register it (or find your receipt) and contact DeWalt via dewalt.com or a DeWalt Service Center.
- Pack is generic / third-party / from eBay: most "DeWalt replacement" packs on Amazon and eBay use counterfeit BMS firmware that doesn't handshake correctly with a genuine DCB115. This is the most common cause of red+yellow with zero actual battery damage.
- Charger is over 3 years old with multiple pack failures: the internal thermistor has likely drifted. A View DeWalt DCB115 Charger on Amazon (paid link) costs less than a pack and is almost always the right call if you've confirmed two or more packs fault on the same charger.
FAQ
Does the DCB115 charge FLEXVOLT (60V MAX) batteries? Yes, but slowly. DCB115 is rated for 20V MAX / 12V MAX / FLEXVOLT, but FLEXVOLT packs charge at their lower 20V MAX rate on this charger. For full-speed FLEXVOLT charging, use the DCB118 fast charger.
Can I leave a battery on the DCB115 after it's done charging? Yes. Once it reaches solid red (fully charged), the charger enters maintenance mode and will not overcharge. Many pros keep their daily packs parked on the charger overnight.
Why does the charger only fault on cold mornings? Lithium-ion BMS chemistry refuses to charge below 32°F. If your charger lives in an unheated garage and you hit it first thing on a winter morning, the pack is often too cold — let it warm indoors for 30 minutes.
Is a swollen DeWalt battery a warranty claim? Usually yes, if you're within 3 years of purchase and the pack hasn't been physically damaged. Swelling is almost always a manufacturing defect in one or more cells. Do not attempt to use or charge a swollen pack — bring it to DeWalt Service or a recycling drop.
Should I buy a third-party DeWalt-compatible battery? We don't recommend it. The counterfeit BMS in most third-party packs is the single most common reason for red+yellow fault codes on otherwise-fine DCB115 chargers. Genuine DeWalt packs work with the 3-year warranty and won't cause handshake failures.