56V EGO CS1400 Chainsaw Replacement Battery 4.0Ah Li-ion

My EGO chainsaw starts fine then bogs down and dies halfway through a thick log — is the battery failing or is something else wrong?

That cutout pattern under load is almost always thermal protection triggering, not a dead cell — the 56V pack pulls hard during a bound cut and the BMS shuts the battery down before anything fries. Let the pack sit off the tool for 10 minutes, then check whether the LED indicator on the battery shows a fault pattern (rapid blinking or no lights); if it recovers and runs normally after cooling, the cells are fine but you're hitting the thermal ceiling. If it shuts off immediately on the next cut without getting hot, put a multimeter on the battery terminals — a healthy 56V ARC Lithium pack should read between 54V and 58.8V at rest.

I put my EGO chainsaw away at the end of the season with the battery in it and now the battery won't take a charge at all — charger just blinks and stops.

Storing a Li-ion pack fully discharged in a cold garage is the fastest way to drop cells below the recovery threshold — the charger blinks and quits because it's seeing voltage too low to safely initiate a charge cycle. Pull the battery off the charger, let it sit at room temperature (above 60°F) for an hour, then try the charger again; some EGO chargers have a recovery mode that kicks in once the pack warms up. If the charger still faults, check the battery terminal pins for corrosion or debris — a dirty contact on a 56V pack can read as an open circuit and trigger the same fault light. A pack that spent the winter deeply discharged and won't recover after warming is genuinely damaged and needs replacement, not coaxing.

My replacement EGO 56V battery fits and powers on but the chainsaw chain feels slow — it ran faster on the old battery even when that one was dying.

A new 4Ah pack running slower than an older higher-capacity battery is usually a capacity mismatch affecting sustained output — the CS1400's brushless motor scales its current draw against available amp-hours, and a 4Ah pack delivers less sustained current under a heavy bar load than a 5.6Ah or 6.72Ah pack would. This isn't a defect; it's physics — check that the battery is fully charged first, because a 56V ARC Lithium pack at 80% charge can feel noticeably sluggish on a chainsaw compared to 100%. If chain speed is still low on a full charge, clean the bar groove and check chain tension — a dragging chain adds resistance that a smaller pack can't overcome the way a bigger one masks it.