Battery will not charge at all and the charger does not respond: sleeping BMS or voltage close to zero

If nothing happens when you connect the charger, the cause may be the socket, the plug or the charger. It may also be the BMS protection after deep discharge, or damaged cells. First, safely check the power supply, connections and charger indicator without opening the battery. If that does not help, the battery voltage must be measured and diagnosed at a service centre.

This advice is based on solutions to specific, anonymised cases handled by Amperi Service. Every case can be different – the steps described do not replace a professional service diagnosis.

Symptoms

The battery does not respond after the charger is connected and charging does not start.
The charger indication does not change (the LED stays off, does not change colour or shows an error).
The charger has been connected for many hours and charging still has not begun.
The battery had previously been completely discharged or left unused for a long time.
A service measurement shows a voltage close to zero or clearly too low, and the BMS is asleep.

Possible causes

No power at the socket, or a problem with an extension lead.
Poor contact in the plug or socket: water, dirt, burn marks, bent contacts.
A faulty charger.
BMS protection after deep discharge or a long period of inactivity: the BMS goes into sleep mode and blocks charging.
A battery temperature that is too low or too high, at which the BMS blocks charging.
A damaged section or damaged cells, or unbalanced cells. The battery voltage is then close to zero or very low.

What you can check

Switch off the vehicle, remove the key and make sure the battery is seated correctly.
Check the socket by plugging another device into it, or use a different socket. Preferably do not use an extension lead.
Check that the charger plugs are pushed fully into the vehicle or battery.
Inspect the sockets and contacts. Look for water, dirt, burn marks and bent contacts. Do not clean anything with metal tools and do not take any housings apart.
Note down or photograph the LED status or the message on the charger (colour, flashing, error code).
If the battery is very cold or very hot, wait until it reaches ambient temperature and charge it at room temperature. The permitted charging temperature range is set by the manufacturer, usually about 0–45°C. Do not charge a frozen battery.
If you have access to a second, working charger suitable for this model, check whether the behaviour changes. This makes it easier to tell a charger fault from a battery fault. Do not use a charger with different parameters or for a different cell chemistry.
Do not try to open the battery, short the contacts or "wake up" the BMS yourself (e.g. by connecting it to another battery or a power supply). Measuring the cell voltage and waking the BMS are tasks for the service centre.
Prepare the details for the service request: vehicle model, VIN, battery serial number (usually on the label on the housing), the charger indication, the circumstances in which the problem appeared (deep discharge, long standstill, moisture, a fall, a change of charger), mileage and purchase date.
If there is smoke, a burning smell, unusual heating of the charger or battery, or a swollen battery housing, stop charging and stop using the vehicle immediately. Disconnect the power only if you can do so safely, and move the battery away from flammable materials. Do not charge a swollen or damaged battery. If a fire is developing or there is smoke, call the emergency services (112).

Follow safety rules when working with batteries and electrical equipment. Do not open batteries or high-voltage electronics. Unauthorised modifications to the equipment during the warranty period may void the warranty.

When to contact the service

Service diagnostics are needed when the socket works, the connections and contacts are fine, and the charger still does not start charging. They are also needed when the battery was completely discharged and connecting it for several hours had no effect. If there is smoke, a burning smell, unusual heating, a swollen housing, or signs of moisture or mechanical damage, stop using the battery without delay and hand it in to a service centre. The service centre measures the battery voltage and checks the BMS state. If diagnostics show damaged cell sections, the repair may include replacing them, balancing the cells and a capacity test. The scope of work depends on the diagnostic result.

FAQ

What does it mean that the BMS is asleep?

The BMS is the system that manages the battery and protects the cells. After deep discharge or a long period of inactivity it may go into sleep mode, cut off the battery output and block charging. From the outside, this looks like a battery that does not respond to the charger.

Why does the charger not respond even though it has been connected for several hours?

The most common causes are no power or poor contact at the plug, a faulty charger, or BMS protection or a very low battery voltage. Leaving it connected longer usually does not change this, so first check the socket, the connections and the charger indication.

Can I measure the battery voltage or open the battery myself?

No. Do not open the battery or interfere with its electronics. Measuring the cell voltage and waking the BMS are done by the service centre.

Does a voltage close to zero mean the battery has to be replaced?

Not necessarily. A very low voltage may result from deep discharge and a sleeping BMS, but also from damaged cells. Only diagnostics show whether, for example, replacing faulty sections and balancing the cells is enough, or whether more extensive work is needed. The longer a battery stays deeply discharged, the higher the risk of permanent cell damage.

How can I avoid deep discharge of the battery?

Avoid letting the battery discharge completely and avoid storing it in that state for a long time. Charge it at room temperature. For longer periods of inactivity, store it partly charged (usually about 40–60%) in a dry, cool place, and check and top it up periodically, following the manufacturer's recommendations.

Problem still there? Open a service request with Amperi Service – we will help.

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Updated: 2026-10-31 · Serwis Amperi · serwis@amperi.eu