Both chargers in CTEK's NXT range do the same fundamental job — keep a battery maintained without overcharging it — but they're built for different scales of vehicle and use case. Here's how to tell them apart.
The core difference is power
The NXT 5 is rated at 5A. The NXT 15 delivers triple that — 15A — which translates directly into how quickly it can bring a battery back up and how large a battery or electrical system it's suited to maintaining. A higher-amperage charger isn't just "faster" in the abstract — it's what makes the difference between comfortably maintaining a small passenger car battery and properly serving a larger vehicle's electrical system.
What the NXT 5 is built for
The NXT 5 covers the fundamentals: automatic maintenance charging for a standard passenger car or performance car battery, sized for owners who want reliable, connect-and-forget protection during storage without needing the higher power ceiling or extra modes the larger unit offers.
What the NXT 15 adds
Beyond the higher charging power, the NXT 15 is built for performance cars, boats, caravans, and larger vehicles — anything with a bigger battery or electrical system than a standard passenger car. It includes automatic temperature compensation, adjusting its charging behaviour to ambient conditions rather than applying a flat charge regardless of heat or cold. It also has a constant supply mode, useful for diagnostic work where a stable voltage needs to be maintained while other systems are being tested. And it includes patented reconditioning, designed to recover batteries that have been allowed to run more deeply discharged than a standard maintenance cycle would address. All of it runs fully automatically and spark-free — connect it and leave it.
How to choose between them
For a standard car battery being maintained through normal storage periods, the NXT 5 does the job it's designed for. Step up to the NXT 15 if the vehicle has a larger battery or electrical system, if the storage period is long enough that reconditioning capability matters as a safety net, if diagnostic-style constant supply is useful, or if there's simply a preference for more headroom and faster maintenance charging.
The takeaway
Neither charger is the "better" one in isolation — they're sized for different jobs. The NXT 5 is the straightforward choice for a standard car; the NXT 15 earns its higher power rating on larger vehicles, longer storage periods, or anyone who wants the reconditioning safety net built in.