Metabo battery won't charge or flashes an error (CAS / LiHD)

You drop a Metabo pack onto the charger, but the green light never comes on — or it blinks red, and the tool stays dead. This is an honest read from the bench on why a Metabo CAS or LiHD battery won't charge or flashes an error: how this system differs from Makita and Bosch, which faults you can clear yourself, and when the pack belongs on the bench for repair or a re-cell. Metabo (and its CAS-compatible siblings — Mafell, Fein, Rothenberger, Eisenblätter) is exactly the edge case that most cordless-tool repair articles leave out.

The Metabo LiHD and CAS system — why it behaves differently

Before you start diagnosing, it helps to understand how your pack differs from an ordinary battery. In its top packs Metabo uses LiHD cells (High Density) — lithium cells with a larger internal surface and lower internal resistance than standard Li-Ion. In practice that means a 5.5 Ah LiHD pack can deliver as much current as a regular 8 Ah pack, in a smaller body. That is good for the tool but harder for diagnostics: these packs are worked harder, run hotter, and their BMS (battery management system) board reacts more sharply to unbalanced cells.

CAS (Cordless Alliance System) is a shared platform — the same pack fits tools from several brands. That means a fault you see on one charger may actually originate in a completely different tool or a different batch of packs. So in Metabo diagnostics we always test the pack and the charger as a pair, never each one in isolation.

The key thing to remember: a Metabo pack is not just a bundle of cells. It carries a BMS board with temperature sensors, cell balancing, current measurement, and an error memory. Most "won't charge" cases are exactly this board's protection kicking in — not dead cells.

The charger blinks: temperature vs cell fault

Metabo chargers (ASC 55, ASC 145, ASC Ultra and similar) signal with two LEDs — usually green and red. Check your charger's housing label for the exact code combination for your model, but every signal falls into a handful of broad categories, and you can read the category without the manual.

A temperature error is the most common and the most harmless. The Metabo BMS will not let a lithium pack charge outside roughly the 0–45 °C range — that is a safety standard for all lithium batteries. If you bring the pack in from a cold van in winter, or it has just been under a heavy load and is hot, the charger will blink red and wait. ASC chargers have active cooling (a fan) that brings a hot pack down — listen for whether the fan kicks in.

A cell or BMS fault is more serious. If the pack is at room temperature, the contacts are clean, but the red is steady and charging never starts — the BMS has rejected the pack. The usual cause is unbalanced cells (one block's voltage has dropped below the threshold) or a deep discharge. That pack won't be revived by the charger; it is assessed on the bench.

The pack won't hold charge or drops power fast

The second common complaint: the pack charges normally (the green light comes on), but it runs for a minute in the tool and cuts out, or the power collapses sharply under load. That is almost always a sign of cell ageing or imbalance, not a charger fault.

How it shows up in practice:

1. The pack reads full but drains quickly. Under a heavy load, LiHD cells reveal their real state — a worn cell's voltage drops fast, the BMS reads it as empty and shuts the tool off for safety.
2. An impact driver or angle grinder "stutters" under load. A textbook single-weak-cell pattern: it runs at no load, but the moment you load it, the voltage in one block sags and the BMS briefly cuts out.
3. The pack heats up disproportionately fast. High internal resistance in a worn cell dumps heat — if one end of the pack is noticeably warmer, that is where the weak cell lives.

With LiHD packs it is typical for two cells out of, say, ten to be more tired than the rest. The BMS balances them up to a point, but once the gap is too wide it can no longer keep up, and the whole pack behaves like its weakest cell. That is exactly where the conversation about a re-cell begins — replacing the cells while keeping the original body and BMS.

Contact and BMS-board faults in Metabo packs

Before you blame the cells, check what is simpler and more often visible — the junction between the pack and the charger or tool.

• Burnt or oxidised contacts. Metabo packs slide onto the tool along rails with gold-coloured contact blades. Dust, metal swarf and damp on them create a contact resistance that heats under load. The tell: the pack works intermittently if you wiggle it. Clean with a dry brush or isopropyl alcohol, never a metal object.
• A loose T-rail. If the pack rocks in the tool, the contacts break instantly and the tool cuts out as if the battery were empty. That is a mechanical defect, not an electrical one.
• A BMS memory error. On Metabo's higher packs (especially ones with a charge indicator and Bluetooth) the BMS stores faults in memory. Sometimes a full charge after a deep discharge "unlocks" the pack, but often the recorded error stays and is only cleared at the service centre with the right equipment.
• Broken leads at the terminals. After a drop or years of vibration, the internal connections at the BMS board tend to crack. The tell: the pack only works in a certain position or after a tap.

This is where self-help ends. You can safely clean the contacts and spot a rocking rail. But do not open the pack yourself: the lithium cells under the housing are charged, a short between blocks produces an arc discharge and a fire risk. A damaged BMS or a swollen cell is a genuine thermal-ignition hazard.

Is a Metabo pack worth re-celling

Re-celling (replacing the cells in the original housing) is often worthwhile on Metabo packs precisely because the body, rails and BMS are well made and expensive — the valuable parts stay, you only swap the tired cells. But it is not always the right call. This table sums up when a re-cell pays off and when it does not; the exact decision is made after diagnostics.

A word on safety and quality: a re-cell must use the same class of cells with a matching discharge current. Drop cheap low-current cells into a LiHD pack and you get a pack that looks full but heats up and collapses under load — exactly the problem you wanted rid of. An honest re-cell keeps the original BMS and balances the new cells; we do not do it with lower-grade cells just because they are cheaper.

If you are wondering how Metabo fits the wider picture, the Makita, Bosch, DeWalt repair comparison is useful — the Metabo CAS system behaves differently, but the principles of cell wear are the same for every brand.

Metabo repair in Riga — what to prepare before your visit

To make the diagnosis fast and honest, bring as much of this as you can:

1. The pack itself (all of them, if several behave the same way — it helps separate the pack from the tool).
2. The charger you see the error on. In the CAS system the charger and pack must be tested as a pair.
3. The tool the pack "won't hold" in — to check whether the fault is in the tool's contacts.
4. A precise description of the error: which LED blinks, how many times, whether the pack heats up, whether the problem follows a specific pack or a specific tool.
5. If the pack has been in the cold or just under a heavy load — mention it, because a temperature error can often be ruled out straight away.

Before the visit, you can safely try this at home: clean the contacts, let the pack reach room temperature, attempt the charge again. If the temperature error disappears — there was no fault. If the red stays steady even at room temperature with clean contacts, the next step is the bench.

A more general approach to charger diagnostics (not just Metabo) is covered in power tool charger not working — start there if you are not sure whether the fault is in the pack or the charger.