12V EGO CHT2001E Replacement Battery 2Ah Li-ion

My CHT2001E cuts fine for a bit then suddenly stops mid-hedge — is the battery dying or is something else shutting it off?

That's almost certainly the battery's thermal cutoff triggering, not capacity failure — 12V Li-ion packs this size protect themselves by cutting power when cell temperature spikes under sustained load, especially on the shrub blade which draws harder than the grass attachment. Let the battery cool completely off the tool, then reattach and try again; if it resumes normally, the cells are fine but you're hitting the thermal threshold. A genuinely failing battery will either not restart at all or restart weak and bog down immediately. Check whether it happens specifically on the hedge blade versus the grass attachment — if it only cuts out on one, that tells you it's load-driven, not a dead cell.

Charged the replacement battery all night and the shears feel noticeably weaker than the original — blade is struggling through anything thicker than soft new growth

A 12V Li-ion pack that reads fully charged but delivers low torque is usually a cell-voltage imbalance issue — one cell in the series stack is dragging the others down, and the tool sees a voltage sag under load even though the resting charge looks fine. We've seen this on new aftermarket packs that shipped partially discharged for months before sale; the weak cell doesn't recover fully on a first charge. Run the battery through two full discharge-and-recharge cycles before writing it off. If the blade still bogs on soft growth after that, measure the battery terminal voltage under load with a multimeter — a healthy 12V Li-ion should hold above 10.5V while cutting; anything below that confirms a weak cell.

The charger light goes solid green almost immediately — way too fast — but the shears barely work

A charge cycle that ends suspiciously fast on a Li-ion pack means the charger detected a near-full voltage at the terminals and quit early — this happens when a cell has internally shorted and is pulling the pack voltage artificially high at rest. The battery looks "full" to the charger but has almost no usable capacity. This is different from a normal fast charge — a genuine 2Ah 12V pack should take close to an hour from flat. Check the battery terminal voltage with a multimeter immediately after the charger goes green; if it reads above 12.6V the charger was fooled, if it reads below 11V you have a shorted or completely dead cell that needs the pack replaced.