Eight Common Signs It Is Time to Replace Your Dyson Battery

Sign 1 — the run time has collapsed against its own history

What it means. Lithium packs do not fail abruptly; they lose capacity gradually as the cells age, so the machine now stops on a charge that used to last the whole house. Your own history is the only baseline worth quoting — Dyson publishes mode-by-mode run times per model, and no two floors are the same.
How to confirm cheaply. Charge fully on ECO, then clean one room and time the machine. Repeat the identical clean on the same floor after a filter wash. If the number has fallen well below what this machine used to give you, and the airway is clear, capacity loss is the explanation.
What to order. A pack in the same voltage platform — or the higher-capacity build on that platform, such as the 4.0 Ah V6 replacement battery (21.6 V, 86.4 Wh) in place of a 3.0 Ah shell.

Sign 2 — it dies on MAX but still finishes the job on ECO

What it means. MAX drives the motor at a much higher current than ECO. An aged pack has rising internal resistance, so its voltage sags under that heavy load and the protection circuit cuts power long before the charge is truly gone. This is one of the most characteristic wear symptoms there is.
How to confirm cheaply. Run a full clean on ECO and note the result, then try MAX on the same floor. If MAX cuts out quickly while ECO still finishes, and the filter is clean, the pack can no longer hold voltage under load.
What to order. The correct platform pack — a bigger-capacity build of another voltage will not fix a load-sagging cell. See the guide to improving V7 run time for the mode habits that stretch a healthy pack.

Sign 3 — it will not hold a charge overnight

What it means. A healthy pack sitting on the dock holds its state of charge for weeks. Self-discharge large enough to flatten a pack overnight points to an ageing cell or a protection board leaking current — the machine may even feel warm when it is doing nothing.
How to confirm cheaply. Charge to full, switch the machine off, leave it off the charger overnight, and check the gauge in the morning. Repeat twice. A pack that loses most of its charge in twelve hours without being used is finished.
What to order. A replacement pack for your platform, plus a charger check — see the 21.6 V and 22.2 V charger listings if yours is original and several years old.

Sign 4 — the charger light never changes

What it means. Charging normally shows a visible state change on the pack or the plug. No change at all usually means power is not getting into the pack: a failed charger, a damaged plug or pin, corroded contacts, or a pack whose protection circuit has latched off. A charger fault looks exactly like a battery fault.
How to confirm cheaply. Try a known-good charger of the correct voltage on your machine; inspect the plug pins and the socket for bent, green or burnt contacts; and test the wall socket with another appliance. Warm the machine back to room temperature if it has been stored in a car or a shed — charging is normally restricted outside a sensible temperature window, and our V10 listing publishes 0–45 °C charging and −20–60 °C discharging.
What to order. Whatever the test eliminates. If the charger works and the contacts are clean, order the pack; if the charger is dead, order the matching voltage-specific charger and keep the pack.

Sign 5 — the pack is hot, smells burnt, is discoloured or has swollen

What it means. This is not wear, it is a fault. Mild warmth after a long clean is normal; a pack that is uncomfortably hot, smells acrid, shows discoloured or bulging plastic, or has a shell that no longer sits flat has an internal problem.
How to confirm cheaply. Do not confirm it — stop. Look at the pack on a flat table, press the case gently (do not puncture anything) and smell near the vents. Any of those three findings ends the diagnosis.
What to order. A replacement pack, and no further charging of the old one. Read the safety block below before you do anything else.

Sign 6 — the machine was dropped, and the fault started that day

What it means. A fall can crack a cell tab, loosen a connector, distort the shell or break the communication path between the pack and the machine. Faults that begin the same hour as an impact are usually impact faults.
How to confirm cheaply. Look for a cracked seam, a chipped corner, a dented face, a loose rattle inside the case, or a connector with a bent pin. Re-seat the pack firmly and check the machine runs; if the fault persists and the damage is visible, treat the pack as damaged rather than worn.
What to order. A new pack. Note honestly that our warranty does not extend to products that are physically damaged or not under normal operating conditions as a result of misuse or improper installation, so drop damage on a replacement is not a warranty claim — it is a new order.

Sign 7 — the pack is simply old, in cycle terms

What it means. Lithium-ion cells are rated for a few hundred full charge- discharge cycles before capacity falls noticeably. A household machine cleaned twice a week uses those cycles up over a couple of years, and heavy MAX-mode use uses them faster.
How to confirm cheaply. Count roughly, not precisely: charges per week multiplied by the number of years you have owned the machine. A pack in the many hundreds of cycles that has been losing run time steadily is at the end of its service life rather than defective.
What to order. The right platform pack from the Dyson battery range; the lifespan guide in Australian conditions explains what to change so the next pack lasts longer.

Sign 8 — the fault travels with the pack, not the machine

What it means. On the models where the pack comes out of the body and the machine runs from a dock or a second pack, you get a real A/B test. If the machine behaves normally with a known-good pack of the same platform — or if your pack behaves badly in somebody else's identical machine — the machine is fine and the battery is the fault. This is the strongest evidence available without test gear.
How to confirm cheaply. Borrow or buy one correct pack, or fit your suspect pack into a friend's same-model machine. Swap tests only work inside one voltage platform: a V6 pack cannot be used to test a V8.
What to order. Once the swap proves it, the pack for your platform. The V7 4.0 Ah pack and the V8 4.0 Ah pack are the two most common answers.