CTEK D250SE 12V Smart Charger 20A


The CTEK D250SE Smart Charger is ideal for RV or other off-grid vehicle owners without access to a mains power supply. This DC-to-DC 20-Amp charger is designed for a dual battery system using a starter battery and service/auxiliary battery. Charge your service battery while on the move!

  • Charge, Condition and Maintain 12V Lithium or Lead/Acid Batteries
  • 20A fully automatic temperature-compensated charging for batteries from 40-300Ah
  • Compatible with both normal and smart alternators
  • Dual input (alternator, solar or both in parallel)
  • Screw terminals make it easy to connect inputs and outputs
  • Selectable lithium and lead-acid mode
  • Solar panel regulator with Maximum Power Point Tracking (MPPT)
  • 5-Step charging program
  • Can be mounted
  • Works great with our V1 and V2 Deep Cycle Batteries

In stock (can be backordered)

SKU: BC-CTK-D250SE Category: Tags: ,


20A Smart DC Charger & Maintainer

The D250SE (CTEK Part No. 40-315) is a DC to DC fully automatic charger that’s designed to charge a Service Battery and is powered by the alternator/starter battery. With dual inputs the D250SE is also solar compatible (a standard solar controller is not necessary). The D250SE charger supplies up to 20A of power to any 12V lead-acid or lithium service battery from 40–300Ah. It also works if the starter battery and service battery are different chemistries, for example if the starter battery is lead/acid and the service battery is lithium. (Note: a service battery may also be called an auxiliary/aux battery, house battery, secondary battery, or backup battery.) This is a great charger for our V1 and V2 Lithium Deep Cycle Batteries.

Dual Inputs

The D250SE CTEK Charger has dual inputs and can charge the service battery from the alternator or a solar panel or both. The charger is designed to work with smart alternators and can still operate if the alternator is shut off but the vehicle has access to solar or wind power. So it can use power from the alternator, solar panel, wind power, or any DC power source can be used through the solar input port (within voltage spec). The D250SE can also charge the service battery from the solar input and the alternator in parallel using its built-in regulator to save fuel.

Optimum Charge

Continuous charging while the vehicle’s on the move means the batteries are fully charged in the shortest possible time. The built-in temperature sensor compensates for hot or cold conditions to prevent the battery from overheating or overcharging, so it always gets the optimum charge.

When the service battery being maintained is fully charged, the D250SE will automatically redirect overflow charge power to top-off the starter battery. The D250SE can maintain a stable output up to 20A to vehicles fitted with smart ECU controlled alternators.

TIP: compliment the D250SE charger with a CTEK Smartpass 120S if the service battery capacity is greater than 100Ah or has parallel consumption while charging is in progress. This reduces the charging time. Together, CTEK’s D250SE and Smartpass 120S are a powerful, flexible 140A off-road solution for battery charging management. Learn more.


5-Step Program

  1. Accept*: Tests if the battery can accept charge. This step prevents that charging proceeds with a defect battery. (*Step 1 for lead/acid is Desulphation)
  2. Bulk: Charging with maximum current until approximately 90% battery capacity*. (80% capacity for lead/acid.)
  3. Absorption: Charging with declining current to maximize up to 95% battery capacity*. (100% capacity for lead/acid.)
  4. Float: Maintaining the battery voltage at maximum level by providing a constant voltage charge.
  5. Pulse: Maintaining the battery at 95–100% capacity. The charger monitors the battery voltage and gives a pulse when necessary to keep the battery fully charged.

Video about D250SE Charger

CTEK's short series of videos about the D250SE as well as the Smartpass 120S


  • CTEK PN: 40-315
  • Input: 11.5–23V, 25A
  • Output: Max 14.4/14.2/14.7V, 20A max
  • Back-Current Drain*: Less than 1Ah/month
  • Ambient Temperature: -4°F to +122°F (-20°C to +50°C)
  • Battery Types: 12-Volt WET, EFB, Ca/Ca, MF, AGM, GEL, Lithium (LiFePO4, Li-Fe, Li-iron, LFP)
  • Battery Capacity: 40–300Ah
  • Insulation class: IP65 (splash and dust proof)

* Back current drain is the current that drains the battery if the charger is not connected to the mains. CTEK chargers have a very low back current.

Note: the recommended solar panel size is 50-300W for this charger.

Check out our Energy Storage products for Solar Panels, Deep Cycle Batteries and more.

Proposition 65 Warning

WARNING: Cancer and Reproductive Harm – www.P65Warnings.ca.gov

Additional information
Weight 5 lbs
Dimensions 14 × 14 × 6 in
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