3.7V Wolf Garten BMZ 1S2P Cordless Tool Replacement Battery

My Wolf Garten tool worked fine for the first few charges but now dies way before the garden bed is finished — is the new battery faulty?

Probably not faulty — 3.7V single-cell Li-ion packs like this one are sensitive to shallow cycling, where repeated top-up charges before the cell fully depletes compress the usable capacity over time. We see this consistently on the bench with low-voltage Li-ion packs in this class. Let the battery discharge further before each charge for several cycles and check whether capacity recovers. If a full discharge-and-recharge cycle doesn't restore normal performance, measure resting voltage after a full charge — it should read at or above 4.1V; anything lower points to a degraded cell.

Replaced the battery and now the tool runs slower than it did with the old one — same voltage, so what's wrong?

A fresh cell can actually expose a weak motor or worn contact points that the old battery, with its higher internal resistance, was masking. It can also go the other way: if the replacement cell's internal resistance is higher than spec, voltage sags under load and the tool bogs down. Check the terminal connections on the battery and tool for corrosion or debris causing a poor contact — that's the first thing to rule out. If contacts are clean, measure voltage under load; a healthy 3.7V Li-ion cell should hold above 3.5V when the tool is running.

The charger light just keeps blinking and never goes solid — it won't charge the new battery at all.

Most chargers in this voltage class run a quick diagnostic before charging and will blink continuously if the cell voltage reads below the recovery threshold, typically around 2.5V. This happens when a new replacement has been sitting in a warehouse and has self-discharged too far for the charger to recognize it as a valid cell. Try leaving the battery connected to the charger for 10–15 minutes — some chargers will trickle charge a deeply discharged cell back into range before switching to normal charge mode. If the light pattern doesn't change at all after that, measure the bare battery terminals with a multimeter; a reading below 2.5V means the charger is working correctly and the cell needs a slow-charge recovery or replacement.