About this replacement
Gardena Cordless Lawn Trimmer — 18V Li-ion Replacement Battery
This 18V, 5000mAh (90Wh) lithium-ion battery fits the Gardena AccuCut cordless blade trimmer range. These trimmers use replaceable 2-inch blades instead of cutting line, so consistent voltage delivery matters — blade engagement drops noticeably when the pack sags under load. Confirmed fit across the 8841, 8840, AccuCut Li 400, AccuCut Li 450, and related models.
- Shared platform compatibility: The AccuCut Li 400 and Li 450 series share the same 18V connector and BMS communication protocol, which is why one pack covers the full model family listed.
- Bench tested on actual hardware: We ran full charge/discharge cycles — the BMS held voltage steady under load and tripped the low-voltage cutoff cleanly without requiring a manual reset.
- First charge on a new pack: Run a full charge before first use. Li-ion cells in storage ship at partial charge, and a complete initial cycle helps the BMS calibrate the state-of-charge reading accurately.
Why capacity matters on blade-style trimmers
Blade trimmers draw current in short, sharp bursts each time a blade contacts thick grass or edging. A higher-capacity pack like this 5000mAh unit maintains a more stable voltage curve across those spikes. Smaller or degraded packs sag mid-session and the trimmer slows noticeably before the battery gauge shows low. The 90Wh rating gives this pack meaningful headroom for that load profile.
Trimmer powers on but cuts weakly — cause and fix
Weak blade force with no error light usually points to a degraded cell group dragging down pack voltage under load. The motor still runs, but doesn't reach full speed. Remove the pack, check the contact pins for corrosion or debris, and seat the replacement firmly until it clicks. If the original pack caused this symptom repeatedly, the cells had likely dropped below the threshold where the BMS could compensate.