2020 Giant E+0 showing red fault light with secondhand 625Wh battery?

[Johnr252]

I’m having issues using a secondhand 625wh battery on my 2020 Giant E+0.
It shows a red fault light after a few minutes riding. It works fine when I use the original 500wh battery.

@Greg Watts

 

[Greg Watts]

Good news first: a 625Wh Giant EnergyPak Smart should be fully cross-compatible with your 2020 Trance E+ / Stance E+ / whichever E+0 you're on. Giant's official line is that the 500/625/750/800Wh EnergyPak Smart batteries are interchangeable across the 2019–2025 platform, so the bike itself isn't the problem. Something about this specific battery is.

A red light + cut-out after a few minutes of riding, that clears when you swap back to the known-good 500Wh, points to one of three things in order of likelihood:

1. Dirty or pitted contacts on the secondhand pack
The 625Wh has been somewhere before it got to you. Vibration on the trail momentarily breaks the connection, the BMS throws a fault, power drops. Pull the battery, inspect the terminals on both pack and bike harness for corrosion, green crust or arcing marks. Clean with isopropyl and a soft brush — no abrasives on the gold pins.

2. A tired/faulty cell or BMS in the used pack
Under load (climbing, Boost mode) a weak cell sags below the BMS cut-off threshold, trips a fault, recovers at rest. Classic secondhand-battery symptom. Test: ride it gently in Eco on the flat — if it holds, but faults the moment you put real current through it, it's the pack, not the bike. @Stihldog has flagged the same intermittent-under-vibration pattern from bad connections too, so don't skip step 1 first.

3. Firmware / generation mismatch
Less likely on a 2020 frame, but worth checking. Get it on the Giant RideControl app (Bluetooth), read the battery's serial/firmware and any stored error codes. If the app reports a specific fault code, that'll tell you definitively whether it's BMS, cell imbalance or comms.

Practical next step: charge the 625Wh fully, leave it overnight, check it still reads full in the morning. A pack that self-discharges noticeably overnight has a cell-balance issue and is the problem. If it holds charge fine, clean the contacts and try again.

One thing worth saying plainly: a secondhand eMTB battery with an unknown history is the single riskiest used component you can buy. If the seller's still reachable, the red-light fault is grounds for a refund.

What error code (if any) does the RideControl app show, and do you know the pack's age/cycle count?

 

[bulek shots]

Speed sensor too far from the magnet
Put some packers between sensor and frame to make it closer to the magnet
It’s Giant design error!

 

[Greg Watts]

Speed sensor too far from the magnet Put some packers between sensor and frame to make it closer to the magnet It’s Giant design error!

@bulek shots - interesting thought, but the speed sensor explanation doesn't quite fit here.

The fault @Johnr252 is seeing only occurs with the secondhand 625Wh battery, and disappears completely when swapping back to the original 500Wh pack.

A speed sensor gap issue would cause problems regardless of which battery is fitted - the sensor doesn't know or care which pack is connected.

That said, you're not wrong that speed sensor gap is a genuine and well-documented Giant/Bosch nuisance.

Good knowledge to have filed away - just not what's causing this particular red light.

For John's specific symptom - battery-dependent fault - the candidates remain a dodgy cell/BMS in the used pack, or a contact issue on the secondhand battery's terminals.