Quick answer: A healthy Level 2 charger adds 25–44 miles per hour depending on amperage. If you're seeing dramatically less, the cause is almost always one of five: (1) the charger's amp setting is lower than you think, (2) the circuit breaker limits it, (3) the vehicle is limiting intake, (4) heat is throttling the session, or (5) shared-circuit load management is splitting capacity. Work the tree below in order — it finds the cause in about ten minutes.
"My Level 2 charger is slow" has a dozen possible causes and one efficient way to find yours: measure, then eliminate. Every step here uses numbers you can read from your charger's app or your car's dashboard — no electrician needed until the tree says so.
Step 0 — Establish your baseline
Expected miles-per-hour by amperage (multiply amps × 240 V × efficiency ÷ your car's mi/kWh):
| Charger current | Power | Typical mi/hr (28 kWh/100mi car) |
|---|---|---|
| 48 A | 11.5 kW | ~37–44 |
| 40 A | 9.6 kW | ~31–37 |
| 32 A | 7.7 kW | ~25–30 |
| 24 A | 5.8 kW | ~19–22 |
| 16 A | 3.8 kW | ~12–15 |
Read your car's current delivery rate (kW) while charging — that single number tells you which branch you're on.
The diagnostic tree
- Check the charger's amp setting: many units default to 32 A or lower until configured up. This is the #1 "slow charger" cause — and free to fix.
- Check the breaker size: a 40 A breaker caps continuous draw at 32 A by code (80% rule). If your electrician installed to the panel's headroom, that's your ceiling — not a fault.
- Check for load sharing: two-charger setups split capacity dynamically; your session slows whenever the second car plugs in. Test alone.
- Check the vehicle's intake limit: some EVs cap AC input (e.g., base trims at 7.2–11 kW) and charge-port temperature derates further in summer — see our heat guide.
- Check the cable and receptacle temperature: warm-but-tolerable is normal; hot plug faces trigger automatic derating. Hot hardware = stop and inspect (see cord safety physics).
- Only now call the electrician: if current delivery matches the breaker math but you expected more, the conversation is about panel capacity — priced in our installation cost guide.
Frequently asked questions
Why did my charging slow down after working fine?
Seasonal heat derating, a firmware update resetting amp settings, or a new load-sharing device on the circuit — re-read the charger app's current setting first.
Does a slow charger damage the battery?
No — slower AC charging is gentler on packs. The cost is convenience, not battery health.
Can I just turn the breaker up?
Only if the wire gauge and charger rating support it — continuous-load rules require headroom, and exceeding them is a fire risk, not a setting.
Is 24 A charging enough overnight?
Yes for most drivers: 19–22 miles/hour × 10 hours = ~200 miles nightly. Match the circuit to reality before paying for amps you don't use.
Freshness note: compiled August 25, 2026. Related: charger comparison, circuit cost guide.