36V EasyRotak 36-550 Bosch Replacement Battery 3.0Ah

My EasyRotak 36-550 cuts fine for the first half of the lawn then bogs down and feels like it's lost power — is that the battery dying?

That's voltage sag under sustained high-draw load — the mower's blade motor pulls hard through thick or damp grass, and a worn or undercharged 36V pack drops below the tool's operating threshold before the charge indicator shows empty. Check whether the battery casing is warm to the touch after it happens; heat means the cells are working at their limit. If you're running one battery back-to-back without a full cool-down cycle, the pack never fully recovers between uses. Charge both batteries fully, let them rest at room temperature for 20 minutes after charging, and check the resting voltage with a multimeter — a healthy 36V Li-ion pack should read between 40V and 42V off the charger.

New battery clicked in fine but the mower just flashes the LED and won't start — no obvious reason why

On Bosch POWER FOR ALL packs, a rapid LED flash on the battery itself (not the charger) usually means the battery management system has triggered a protection lockout — most commonly from a deeply discharged state if the pack sat in storage. Put it on the charger and watch what the charger light does in the first two minutes: a solid fault light means the cell voltage has dropped low enough that the charger won't begin a normal charge cycle. Some chargers in this system have a recovery mode — leave the pack connected for 30 minutes even if the fault light is on and check whether it transitions to a normal charge. If the charger light never changes, measure voltage at the battery terminals; anything below 30V on a 36V Li-ion pack indicates deep discharge that may require a recovery charge cycle.

Grass clippings are shorter but the mower keeps cutting out on slopes — runs fine on flat ground

Slopes increase the load on the blade motor significantly because the mower is also fighting gravity and wheel resistance, which pushes current draw high enough to trip the battery's thermal cutoff — especially on a warm day or with a partially charged pack. The cutoff is a protection feature, not a fault, and the mower will restart once the pack temperature drops. Let it sit on flat ground for several minutes with the battery in place before trying again. To confirm it's thermal cutoff and not a capacity issue, run the mower on flat ground until the same cutout happens — if it doesn't, the slope load is the cause, and running a fully charged higher-capacity pack like this 3.0Ah unit instead of the stock 2.0Ah will give the motor more headroom before the cutoff triggers.