Bosch Charger Steady Red — Battery Defective

What Does This Error Mean?

A steady (not flashing) red LED on a Bosch charger means the battery has been rejected — usually because cell voltage is too low to recover, or one or more cells have failed.
Try the battery on a different Bosch charger to confirm.
If the second charger also shows steady red, the battery is at end of life.
Bosch lithium packs are designed for around 1,000 charge cycles — past that, this is the failure mode.

Affected Models

Bosch GAL 18V Charger
Bosch AL 1820 CV
Bosch GAL 18V-160
Bosch 18V GBA Battery System
Bosch Professional 18V

Common Causes

Battery deeply discharged — voltage too low for the charger to wake it (sometimes recoverable)
One or more cells failed internally — battery management system locks the pack out
Battery aged beyond useful cycle life
Battery damaged by impact or moisture ingress
Charger fault (rare — try a different charger to rule out)

How to Fix It

Try a different Bosch charger.

Borrow another Bosch 18V charger if you can.
If both chargers show steady red on the same battery, the battery is the issue.
If only your charger shows red and a different one charges normally, the charger is faulty — replace the charger, not the battery.
Try a different Bosch battery on your charger.

Same logic in reverse.
A different battery charging normally on your charger confirms the original battery is dead.
The charger is fine — just the one battery has failed.
Check the battery contacts.

Look at the metal contacts where the battery meets the charger.
Dust, corrosion, or sawdust can prevent good electrical contact and trigger steady red.
Wipe the contacts with a dry cloth — sometimes that's enough.
Check the battery age and cycle count.

Bosch batteries are rated for around 1,000 charge cycles.
If you've been charging weekly for 2+ years, you're approaching that.
Once the BMS detects cell imbalance or capacity loss past threshold, it locks the battery out — that's steady red.
Replace the battery.

If the battery is genuinely dead, Bosch 18V replacements are $50–$120 depending on capacity.
Don't try to revive a battery showing steady red — the BMS has flagged it for safety reasons.
Forcing charge can be dangerous and probably won't work anyway.

Frequently Asked Questions

Can a deeply discharged Bosch battery be revived?

Sometimes — if the discharge was recent and one or two cells haven't gone too low.
Some Bosch chargers have a recovery mode that wakes deeply discharged packs.
But if the battery's been sitting empty for months, the cells are usually past saving — the chemistry doesn't tolerate long-term zero charge.

What's the difference between steady red and flashing red on Bosch chargers?

Steady red = battery defective, won't charge at all.
Flashing red = temperature out of range, will charge once temperature is right.
Flashing usually clears with cool-down or warm-up.
Steady is a hard fault — the battery management system has decided this pack is done.