Robomow City 120 Replacement Battery 24V 20000mAh SLA

Robomow City 120 — 24V Sealed Lead Acid Replacement Battery (MRK0041A / MRK0037A)

This is a 24V, 20000mAh (480Wh) sealed lead acid battery for the Robomow City 120 robotic lawn mower. It replaces OEM parts MRK0041A and MRK0037A. The City 120 draws power from this pack to run the blade motor, drive motors, and onboard control system through its full mowing cycle.

• City 120 fitment: Both MRK0041A and MRK0037A are factory battery part numbers for this platform. The City 120 uses a 24V system throughout — blade motor, drive train, and control board all run off the same pack. Voltage, terminal layout, and physical dimensions match the OEM tray exactly.
• Bench tested on actual hardware: We ran load cycles simulating the blade motor inrush current and drive motor draw simultaneously. The sealed lead acid construction handled repeated start-stop sequences without voltage collapse, and the terminals held steady contact throughout.
• Winter storage tip: Sealed lead acid batteries lose charge slowly during storage and can sulfate if left fully discharged. Before reconnecting after months in a garage, put the battery on charge for a full cycle before installing it — connecting a deeply discharged pack directly to the mower may cause the charger to reject it.

Charger showing fault after the City 120 sat in the garage all winter

Sealed lead acid batteries self-discharge at roughly 3–5% per month at room temperature — faster in cold garages. A pack left sitting from autumn through spring can drop below 20V, which puts it below the charger's acceptance threshold. Most Robomow chargers use a voltage-sense gate at startup and will refuse to charge a pack that reads too low. The fix is a slow external charge with a compatible 24V SLA charger that has a recovery or "boost" mode — once the pack climbs back above approximately 22V, the standard charger will accept it again.

Mower cuts out mid-row then resumes on its own

This is thermal protection activating, not a battery fault. When the City 120 drives through thick or wet grass, the blade motor draws significantly more current than on a dry, light lawn. Sustained high draw heats the battery internally, and the protection circuit cuts output until temperature drops. The mower typically recovers within five minutes once parked on flat ground. If this happens repeatedly, clear the cutting area of debris and avoid scheduling mowing sessions immediately after rain — wet grass resistance is the primary trigger.