GS500 3.6V Cordless Grass Shear Replacement Battery 2200mAh

My GS500 grass shear cuts for about 30 seconds then stops like the battery died but the charger says it's full — what's wrong?

This is a classic shallow-cycle problem with NiMH packs: the cells charge to full voltage quickly but have almost no usable capacity left because they've been stored or cycled in a partially discharged state. The battery management circuit reads voltage, not true capacity, so it reports "full" while the cells are effectively empty. Run the new pack through two or three full discharge-and-charge cycles before judging it — let the shear run until it slows noticeably, then charge completely. After conditioning, check that open-circuit voltage sits between 4.2V and 4.5V across the pack terminals before you write it off.

The replacement battery fits in the GS500 but the shear runs way slower than it used to with the original pack — is that a voltage sag issue?

Yes — at 3.6V and low cell count, NiMH packs are extremely sensitive to internal resistance, and a new pack with slightly higher resistance than spec will sag under the load of the cutting blade and deliver less actual power to the motor. We've seen this on the bench with Sub-C NiMH cells that test fine at rest but drop significantly under even a light grass-cutting load. First, confirm the pack has been fully charged for the complete cycle the charger requires — an undercharged NiMH pack at this voltage will feel sluggish immediately. If full charge doesn't fix it, measure pack voltage under load with a multimeter; it should stay above 3.0V while the blade is spinning.

Brand new battery for the GS500, charged it overnight, used it once in the garden, now it won't hold a charge at all — did I kill it?

NiMH cells at this voltage class are vulnerable to voltage reversal damage if one cell in the three-cell pack discharges faster than the others — a single deep-discharge session can permanently reverse one cell and collapse the whole pack. Leaving a NiMH pack on a dumb charger overnight before the first use can also cause mild overcharge damage that shortens life immediately. Check resting voltage across the pack: a healthy fully-charged 3.6V NiMH should read between 4.2V and 4.5V; anything below 3.6V at rest means at least one cell is already compromised. Going forward, charge only until the charger indicates complete, then remove the pack.