Sterling Power Saturn BB1240 Battery-To-Battery Charger - 12V/12V 40A

  (1 Review)
Price:  £307.88   (£256.57 Exc. VAT)

Product code:  P03193
Brand:  Sterling Power
Voltage  12-12V
Current Rating  40A



2 in stock

Sterling Power's revised Saturn range of Battery-To-Battery (DC-DC) chargers have been completely re-designed to make them simpler to use, more compact and easier to install, with a minimal amount of setup. They provide all the features of the previous generation but in a much more user-friendly package.

Compatible with both 'smart' and standard alternators, this 40A input battery-to-battery charger is powered from your vehicle's alternator and delivers the correct charging voltage for your lead-acid or lithium battery. This new model features a vibration sensing mode, meaning that the charger will begin operating when the internal accelerometer detects vehicle movement. This eliminates the need to run a cable to supply an ignition or D+ alternator signal as is required on some other DC-DC chargers. An ignition feed option is still available should the vibration sensing not be suitable for your particular application.

This 40A model also features a bi-directional or 'reverse charging' feature whereby surplus current supplied to your leisure/house battery is passed to the starter battery to charge and maintain it. This is ideal when you are charging your leisure battery from shore/grid, solar, wind or generator power, and ensures that your starter battery is always kept in optimum condition.

The charger comes with a temperature sensor (optional fitment) that allows for temperature voltage compensation for lead-acid batteries, 0°C trip for lithium charging and high temperature trip protection. This unit also features a lithium battery BMS 'wake-up' function to enable your lithium battery to start accepting a charge if the BMS has put it into shut-down mode due to over-discharge.

An optional remote display not only allows you turn the unit on or off remotely, it also provides several additional advanced features such as custom charging profiles, current reduction and charging current and voltage display.

If you require a higher charge current (and your alternator can support it) then any of the units in this new charger range can operate in parallel (e.g. BB1240+BB1240 to provide 80A input, or BB1240+BB1270 to provide 110A input), providing you with redundancy and flexibility in power.

Sterling recommends connecting using 10mm² cable and 50A fuses (see related products below).


  • 4 stage DC-DC battery charging
  • 40A Input - current limiting
  • Bidirectional charging - enables starter battery charging
  • 6 selectable charge profiles for all battery types including lithium
  • 95-98% efficient using buck boost technology
  • Compatible with both smart alternators (Euro 6) and standard alternators
  • 3 charger control modes: Ignition | Vibration | Voltage Sense
  • Automatically recoverable protection for various conditions (see 'Specifications' tab)
  • Multiple units can be wired in parallel to increase output

Further information

Important: Please ensure that your alternator is capable of providing sufficient charge output so that it is not over-worked (which may lead to premature failure). Sterling recommends an alternator output of 50A +

  • Input voltage range: 9V-16V DC
  • Nominal output voltage: 12V DC
  • Continuous rated input power: 42A @ 13.68V (approx. 575W)
  • Continuous rated output power: 38A @ 14.41V (approx. 550W)
  • Efficiency: 95-98%
  • Standby current: 5mA
  • Under voltage protection: Yes (auto-recovering)
  • Input over voltage protection: Yes (auto-recovering)
  • Output over voltage protection: Yes (auto-recovering)
  • Over current protection: Yes (auto-recovering)
  • Over temperature protection: Yes (auto-recovering)
  • Operating temperature: -20 to +60°C
  • Cooling method: Variable speed fan (thermostatically controlled)
  • Max. cable size: 10mm²
  • Overall dimensions: 150 (L) x 130 (W) x 56 (H) mm
  • Weight: 0.8kg
  • Approvals: CE, UKCA, E-marked

Part Number:  BB1240

Average Rating (1 Review):  
Write a Review and share your opinions!

1st time installing the new Style Sterling B2B
09 June 2024  | 

I purchased this particular DC-DC charger because my client was going to have 570w of solar on his van roof and wanted to charge his cranking battery as well as his 3x 120ah AGM leisure batteries. I looked at fuel output MPPT controllers but nothing was big enough for his panel.

The “reverse charge” feature on this unit allows for excess power in the leisure batteries to charge the cranking battery. This seemed ideal. I only went for the 40A as it was the 2nd cheapest one and the client does long journeys.

Compared to previous generations of Sterling chargers, this one has a very simplified set up. Selecting the battery type is easy (although having to count the seconds yourself rather than the LED flashing the seconds for you, as on previous generations, is a tad arduous).

There is no “pure ignition” mode, only volt sense + ignition, volt sense, or volt sense + vibration detect (I wanted to try this but the unit is fitted in the back of the van) I used the volt sense only option and did not run an ignition live wire (2013 Fiat Ducato Euro 5, the alternators on these are fairly traditional)

I did have a bit of a headache trying to get the unit to turn on when the engine was on. Although when I pushed the button, the LEDs would show the battery type, none of the status LEDs lit up. The remedy to this was to disconnect the cranking positive feed (while the engine was running) and reconnect it. This woke the unit up and it’s works as it should ever since.

I normally comm all the negatives to the body (even though Sterling’s instructions are adamant you shouldn’t), this time I did run an additional earth from the cranking battery (I thought it might have something to do with the non start issue). In my testing it seems that both negative terminals on the unit are commed together so (in theory) you only need one negative.

Overall, I like this unit, it’s nice and compact and if I need to, I will use one again. Hopefully, one of the higher amperage ones

Sterling Power

Sterling Power Products is at the forefront of battery charging and power management technology for both the professional and recreational consumer, with many years’ experience. Providing a vast range of products and solutions, this UK-based company uses its award-winning charging technology to minimise re-charge times and maximise service life by ensuring the optimum charging profiles for your battery system. Sterling Power Products is an extremely well known and trusted brand within the marine electronics market and offers a large range of DC-DC charging solutions for the automotive sector.

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