Charging Deep-Dive

Charging Explained

Learn how Li-ion charging works, interpret charging logs, and understand Zero's recommendations for battery longevity.

Last updated: February 5, 2026

TL;DR

Li-ion batteries charge in two phases: Constant Current (CC) for bulk charging, then Constant Voltage (CV) as cells approach full. For longevity, charge to 80-90% for daily use and avoid leaving the battery at 100% or 0% for extended periods.

Charger Differences: Gen2 (S, SR, FX...) uses onboard Calex/Meanwell chargers (1.3-3kW). Gen3/FST (SR/F, SR/S) includes Level 2 J1772 standard and optional Rapid Charge Module for 6kW+ charging.

CC/CV Charging Process

Lithium-ion batteries use a CC/CV (Constant Current / Constant Voltage) charging protocol to safely and efficiently charge cells:

1
Constant Current

Charger delivers maximum current while voltage rises. This is the "bulk" charging phase — fastest rate of charge.

Typical: 0% → ~80%

2
Constant Voltage

Voltage held at max (4.2V/cell), current tapers down. This "absorption" phase tops off cells safely.

Typical: 80% → 100%

3
Termination

Current drops below threshold (C/20 or similar). BMS signals charge complete.

Log shows: Charged To Full

Interactive CC/CV charging curve — hover to see values

SOC (%)

Current (A)

Voltage (V)

CC→CV transition (~80%)

Notice: In CC phase, current is constant and SOC rises quickly. In CV phase, voltage is constant but current tapers — the last 20% takes as long as the first 80%!

Zero Charging Hardware

Charger Type	Power	0-95% (14.4 kWh)	Compatible Models
Standard Onboard	1.3 kW	~9-10 hrs	All models (Gen 2+)
FX/FXE Onboard	0.65 kW	~9 hrs (7.2 kWh)	FX, FXS, FXE
Charge Tank Accessory	+1.3 kW	~4.5 hrs	S, SR, DS, DSR (Gen 2/3)
SR/F Onboard	3.0 kW	~4 hrs	SR/F, SR/S
Level 2 (J1772)	Up to 6 kW	~2 hrs	SR/F, SR/S, DSR/X (standard)
DC Fast (CHAdeMO)	Up to 6 kW	~1 hr	DSR/X only

Times are approximate and assume 10-95% SOC. Actual charging times vary with ambient temperature, pack temperature, and starting SOC. Charging slows significantly above 80% (CV phase).

Level 2 Charging (J1772)

SR/F, SR/S, and DSR/X models include Level 2 charging capability as standard. This uses the J1772 connector found at public EV charging stations and home EVSE units. Maximum charge rate is 6 kW when using a compatible EVSE.

For detailed charger specifications, see the ZeroManual Chargers page and official Zero charging recommendations.

Best Practices for Longevity

Do

• Charge to 80-90% for daily use
• Store at 50-70% SOC for extended periods
• Charge in moderate temperatures (15-35°C)
• Let the bike cool after hard riding before charging
• Use a timer to stop at target SOC if needed

Avoid

• Leaving at 100% for days/weeks
• Letting SOC drop below 10%
• Charging in extreme cold (<0°C)
• Charging immediately after high-temp riding
• Frequent DC fast charging if avoidable

Why 80%?

Li-ion cells experience accelerated degradation above ~80% and below ~20% SOC. The last 20% of charge also takes disproportionately longer due to the CV phase. Charging to 80% gives you most of the range with less wear and faster charge times.

Charging in Your Logs

Look for these indicators in your BMS logs during charging:

Field/Event	Meaning
M:Charge	Active charging session
Charged To Full	Charge completed (100% SOC)
I: -15A	Charging current (negative = into battery)
SOC rising	SOC increasing over time
PT/BT	Temperature during charge (should stay <45°C)
B	Cell balance — may increase then stabilize

Sources:

Battery Basics Next: Riding & Regen

Charging recommendations are general guidelines. Always follow your Zero Owner's Manual for your specific model.