Why won’t my cordless drill battery charge on the dock and what can I try before replacing it?

Blinking on most drill chargers usually means the charger sees a fault or a battery that is too low for a normal charge. You already tried a different outlet, cleaned the contacts, and let the pack cool, so the next step is ruling out charger versus battery. Check the sticker on the charger because different blink speeds often mean temperature wait versus defective battery.

First, borrow a known good battery from the same brand and see if your charger tops it off. If it does, your pack is the culprit. If it also blinks, the charger is bad. If you have a multimeter, measure the battery at the main plus and minus terminals with the pack off the charger. A healthy 20 volt class pack at rest usually lands in the mid to high teens. If it reads near zero, the protection circuit has opened or the cells are deeply discharged and most chargers will refuse to recover it. You can try a gentle wake up by seating the pack on the charger for 10 seconds, removing it for 10 seconds, and repeating a few times, then leave it for 15 minutes to see if the light changes. Stop if the pack warms or smells, and skip any jump start tricks since that is unsafe with lithium packs.

If you confirm the pack is done or just need a quick working setup, a budget drill kit that includes a fresh battery and charger is an easy fix. AVID POWER 20V MAX drill kit solves it because it gives you a new 20 volt battery with a matching charger to cross check whether your old charger or pack was at fault. The 20V MAX platform and the included battery and charger let you get back to work right away while you decide whether to rebuild or replace your original pack.

Easy way to get certainty without buying parts — Take your battery and charger to a neighbor coworker, or a tool library and try cross charging with a compatible pack or charger from the same system. Most home centers will also let you test on a floor model if you ask nicely. If their charger brings your pack back, yours is bad. If your charger brings their pack up, your battery is done. And if neither works together, you have both a weak battery and a touchy charger, which does happen after years of hard use. No cost.

One wrinkle is chemistry. If your tool is older and still on nickel packs, a long sit can push cells so low the charger will balk, but the repeated short seat trick can sometimes bring them back because the charger applies a tiny precharge. If your pack is lithium, do not attempt any jump start or external trickle, the built in protection is there to prevent a dangerous charge on damaged cells. Either way, a test with a known good battery or a quick voltage check tells you what you need. If it is at or near normal resting volts and still refuses to start charging, the charger is the likely fault.

Before buying anything check the age of the battery. Many brands warranty batteries for two or three years and will replace ones that refuse to take a charge, especially if the charger shows a fault blink. Support will usually ask for the blink pattern so read the chart printed on the charger and take a photo which, yeah they may also have you try a charger reset and a different pack if you have access to one. If you are out of warranty, a shop that sells that brand will often let you drop your pack on a display charger for a minute to confirm whether the pack wakes or the charger is the problem so yeah free diagnosis beats guessing. Worth a call.

Super quick checklist you can run which, yeah... unplug the charger for a minute to clear faults. Bring the battery to room temperature and leave it there for an hour if it lived in a hot truck or an unheated garage. Reseat the pack firmly and watch whether the blink is slow or fast, then check the charger label to decode it. Try the ten second on ten second off routine a few times and let it sit. If you have access to a working pack or a working charger from the same line, swap and you will know in minutes. If your pack reads near zero on a meter or starts to warm while still blinking, retire it.

Been there. On most brands a steady blink means the charger either thinks the pack is too cold or hot or that the voltage is below its safe start point. Kill power to the charger for a minute to reset its brain plug back in, then give it one clean seat and watch for a change in the blink pattern. If you can borrow a battery from the same platform, that is the quickest way to split the blame between charger and pack without guessing. With a multimeter, check your pack at the main blades off the charger. A healthy 18 to 20 volt class pack at rest should be somewhere in the mid teens. If it reads close to zero the protection circuit is open and most chargers will never start. One last safe trick is the on off reseat rhythm for a minute or two then leave it to sit on the charger for fifteen minutes. Stop if it warms or smells. If none of that moves the needle, call it failed.

Inspect the small center pin for the temp sensor since a low or dirty pin can make the charger blink endlessly. Gently raise it if needed and clean both pin and pad, and check for cracked plastic so it can charge normally.

If you have a meter and are comfortable using it, you can also test the charger side. Some smart chargers will show a small standby voltage at the big terminals with no battery, others show nothing until they sense the temp pin. That is normal. What you want to see is that the terminals are clean, not burnt, and springy. Next, measure the battery main blades and watch whether the voltage jumps a little when you click it on the charger and then pull it off. If it never budges and the charger blinks the same with any pack you try, the charger controller likely failed. don't open the battery pack to replace fuses or cells unless you are set up for it, the risk is not worth it. Fair warning.

Check that the charger behaves normally with no battery, then meter the pack at the main terminals.

Readings in the teens usually recover after a few short on and off tries while near zero means the pack is locked out, never jump or bypass, and if a known good pack still makes it blink the charger is likely bad.