Choose a charger by your battery, not the box
Two numbers decide it: the charge current, which sets how long a recharge takes, and the largest battery the maker rates the charger to recharge. Everything else is detail.
Checked against sources on by the TrueAmps editorial team.
| Charger | Amps | Recharges up to | 50 Ah from half | Lithium | UL 1236 |
|---|---|---|---|---|---|
| NOCO GENIUS1 | 1 | 30 Ah | maintain only | Yes | Listed |
| Battery Tender Junior Multi-Chemistry | 1 | not published | 38 h | Yes | Listed |
| NOCO GENIUS2 | 2 | 40 Ah | maintain only | Yes | Listed |
| NOCO GENIUS2D | 2 | 40 Ah | maintain only | No | Listed |
| NOCO GENIUS5 | 5 | 120 Ah | 7.5 h | Yes | Listed |
| NOCO GENIUS10 | 10 | 230 Ah | 3.8 h | Yes | Listed |
Read the Ah on your battery first
The capacity is printed on the battery label in amp-hours. NOCO rates the GENIUS1 to recharge up to 30 Ah, the GENIUS2 and 2D up to 40 Ah, the GENIUS5 up to 120 Ah and the GENIUS10 up to 230 Ah. All of them are rated to maintain batteries of any size.
So a small charger on a big battery is not wrong, it is a maintainer. If you want to bring a flat car battery back in an evening, look at the 5 and 10 amp rows. The calculator gives the time for your exact battery.
Specific jobs
- AGM batteries: which chargers have an AGM mode and what it changes.
- Motorcycles and powersports: small batteries, lithium, winter storage.
- Leaving a charger connected: trickle chargers and maintainers are different things.
- NOCO GENIUS lights: what red, green and the error LEDs mean.
- Battery Tender lights: red or amber, flashing or solid, and what to check when it will not turn green.
Compare two chargers
Questions people ask
What size battery charger do I need?
Match the charger's recharge rating to the Ah on your battery label. NOCO rates the GENIUS1 up to 30 Ah, the GENIUS2 and 2D up to 40 Ah, the GENIUS5 up to 120 Ah and the GENIUS10 up to 230 Ah.
Can I leave a smart charger connected all the time?
For the GENIUS1, NOCO's manual says it can be left connected to the battery indefinitely: after a full charge it keeps monitoring and maintaining the battery.
What amp charger is best for a car battery?
It depends on how fast you want it back. By NOCO's charge-time ratio a 50 Ah battery from half charge takes about 19 hours at 2 A, 7.5 hours at 5 A and 3.8 hours at 10 A.
What do the lights on a NOCO GENIUS mean?
Pulsing red on a GENIUS1 means under 75 percent and charging; solid green means full. Our GENIUS lights page covers every light and error.