Mowox BA 515 20V Cordless Lawn Mower Replacement Battery 4900mAh

Mowox RM 1000 WIU-SN Series — 20V Li-ion Replacement Battery (BA 515)

This 20V 4900mAh Li-ion battery replaces the OEM BA 515 pack on Mowox cordless rotary mowers. It fits the RM 1000 WIU-SN, RM 500 WiU-SN, RM 750 BTU-SN, and Silaro Robotic models. Voltage and connector match the original — the mower deck sees no difference at startup.

• RM 1000 WIU-SN family compatibility: These models share the same 20V battery bay, connector pinout, and BMS handshake protocol. One replacement pack covers the full lineup without any adapter or wiring change.
• Bench tested on actual hardware: We cycled this pack through repeated blade-start events, including simulated heavy-load draws that replicate thick-grass cutting. The BMS held stable across all test cycles and cut off cleanly at the low-voltage threshold without latching faults.
• Seasonal storage tip: Before first use of the season, bring the battery indoors overnight if temperatures are below 10°C. Cold Li-ion cells have higher internal resistance, and the blade motor inrush current can trip the BMS on a cold pack before it has a chance to warm up.

BMS cutoff on thick-grass and wet-grass blade load

The RM 1000 WIU-SN blade motor draws a short inrush spike every time it bites into dense or wet grass. If the BMS reads that spike as an over-current event, it shuts the pack down as a protection measure. A new battery sees this more often in the first few cycles because the cells haven't settled into their operating impedance yet. After 3–5 full charge and discharge cycles, the internal resistance drops and the BMS handles those spikes without tripping.

Charger showing a fault light after the mower sat all winter

If the pack sat discharged through winter, the cell voltage may have dropped below the charger's acceptance threshold — typically around 2.5V per cell on a 5-cell 20V pack. Most Mowox chargers refuse to begin a charge cycle below that point and flash a fault or red indicator instead. To recover the pack, check cell voltage with a multimeter across the battery terminals. If you read above 12V total, the charger should accept it after a full power cycle of the charger unit; if it reads below 10V, the pack has self-discharged too far for the standard charger to recover.