You slide the battery onto the charger, the LED starts flashing red, and nothing charges. Before you decide the pack is dead, it helps to understand what that light is actually doing. A Worx charger runs a safety check before it sends any current: it reads the pack's temperature and voltage, and if either is outside the window the charger considers safe, it refuses to charge and flashes red at you. So the flashing light isn't a verdict. It's the charger saying "not right now," and the reason is usually one of four things. Let's go through them in the order they actually happen.
1. The pack is too hot or too cold
This is the most common cause, especially in July. Run a Worx mower or string trimmer hard, pull the pack, and stick it straight on the charger, and you'll get a red flash nearly every time. Lithium-ion cells charge safely only inside a moderate temperature band, and Worx's own support guidance says to let an overheated pack cool to roughly 108°F (42°C) before the charger will accept it.
The fix costs nothing. Set the pack in the shade indoors for 30 to 60 minutes, then try again. In winter the same interlock works the other way: lithium-ion packs won't charge below about 32°F (0°C), so a battery left in a freezing garage gets rejected until it warms up. That's normal protection, not a defect, and no amount of reseating will hurry it along.
2. Dirty or poor contact
If the pack is at room temperature and still flashes red, look at the metal terminals on both the pack and the charger. Grass clippings, sawdust, and oxidation all get between the contacts, and a marginal connection reads as a fault. Wipe the terminals with a clean, dry cloth, rub stubborn oxidation gently with a pencil eraser, and reseat the pack firmly. It sounds too simple to matter, but on outdoor equipment it fixes a surprising share of these.
3. The pack drained too far
Here's the one that catches people after winter storage. Leave a 20V pack sitting in a tool for six months and its voltage can sag below the floor the charger is willing to work with. The charger sees a suspiciously low voltage, assumes damaged cells, and flashes red rather than force-charging it.
Two things worth trying. First, leave the pack on the charger and watch the light: some Worx chargers try to repair a deeply drained pack for about 30 minutes, shown by a flashing green LED, and if the light turns solid red the pack is considered dead. Second, reseat the pack once, firmly, to make sure the contacts are seated. You'll see people online jump-starting a dead pack from a healthy one with wires. Skip that. Pushing uncontrolled current into a lithium pack with no charger logic in the loop is how garages catch fire, and if the pack is that far gone it isn't trustworthy anyway.
4. The pack (or charger) is genuinely done
If the battery is at room temperature, the contacts are clean, and it still flashes red after the recovery attempts, isolate the fault. Put a known-good battery on the same charger: if that one charges fine, the problem is the pack. If a healthy pack also flashes red, the charger is the culprit, and a replacement charger is a lot cheaper than a battery.
Signs a pack is truly finished rather than just cranky: it's swollen, it gets hot doing nothing, it was dropped hard, or it charges but dies in minutes under load. A swollen or damaged pack should not go in a retail drop-off bin or the trash. Take it to a household hazardous waste facility.
One platform note before you buy
Worx runs on the 20V PowerShare system, and the sharing is real: the same 20V pack fits the drills, the trimmers, and the blowers, and the 40V tools run on two 20V packs installed together. What doesn't work is anything cross-brand. A Worx pack fits Worx tools, full stop. If you're replacing, buy the genuine pack or a charger from the same platform, and register it: Worx covers batteries for 3 years with registration and 24 months without, per its warranty page.