About this replacement
iRobot Looj 125 / 135 / 155 — 7.2V Ni-MH Replacement Battery (14501)
This is a 7.2V, 3600mAh Ni-MH replacement battery for the iRobot Looj 125, Looj 135, and Looj 155 gutter cleaning robots. It matches OEM part number 14501 and slots into the same bay as the original pack. The Looj's auger motor and drive system pull directly from this cell stack during operation.
- Looj 125, 135, and 155 compatibility: All three models share the same 7.2V Ni-MH cell configuration, battery bay dimensions, and connector pinout. The same pack runs across the full Looj lineup because iRobot kept the power architecture consistent between generations.
- Bench tested on actual hardware: We cycled this pack through repeated auger-load tests. The BMS held voltage steady under drive motor start-up current and recovered cleanly after sustained resistance from debris simulation. No premature cutoff was observed during normal gutter-pass workloads.
- Looj storage between seasons: The Looj typically sits unused for months at a time. Store Ni-MH cells at roughly 40–60% charge between gutter seasons — a fully charged Ni-MH pack left idle for months self-discharges faster and can cause the charger to read the pack as faulty on the next use.
Why the Looj auger slows or stalls before the battery indicator drops
Ni-MH voltage sags under heavy auger load even when cell charge remains high. When the Looj hits a compacted leaf dam or wet debris, the auger motor draws a spike of current that temporarily drops cell voltage below the drive circuit's operating threshold. The robot reads this as a load fault, not a battery fault, so the indicator stays green while the auger loses torque or stops. A replacement pack with full cell capacity handles these load spikes with less voltage sag and holds the auger at working speed longer.
Looj won't start after sitting all winter — even on a full charge
A Ni-MH pack stored fully discharged for several months can drop below the charger's minimum detection voltage. The charger sees a pack that looks dead and refuses to start a charge cycle. This is a BMS re-initialisation issue, not a charger fault. If the replacement pack also shows this behaviour after storage, connect it to the charger for at least 30 minutes — some chargers require a resting voltage of at least 5.5V before the charge cycle triggers.