STERLING BB1240 Bidirectional Battery to Battery Charger 12V / 40 A

Name: BB1240 Bidirectional Battery to Battery Charger 12V / 40 A
Brand: STERLING
Price: 326.95 EUR
Availability: InStock
Rating: 5 (3 reviews)

SVB item number: 33347 Manufacturer no.: BB1240

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SPYRIDON M.: "Amazing unit - This is the best purchase i have ..."

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The STERLING B2B chargers are highly efficient and feature a compact and lightweight design with an efficiency of between 95-98%. The battery is designed to charge bidirectionally, which means it can use the leisure battery to allow energy to flow back to the starter battery, so that your engine is always ready to start. Product details

only €326.95

VAT inc., ex-works

5 | in stock

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Available variants

STERLING BB1225 Bidirectional Battery to Battery Charger 12V / 25 A

only €217.50

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STERLING BB1270 bidirectional battery to battery charger 12V / 70 A

only €436.50

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STERLING BB12120 bidirectional battery to battery charger 12V / 120 A

only €749.95

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STERLING BB12200 bidirectional battery to battery charger 12V / 200 A

only €1,089.95

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STERLING BB1224120 bidirectional battery to battery charger 12V / 24 V / 120 A

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At a glance!

Max. charging current: 38 A

Bi-directional charging

Optional remote display / operation

Temperature sensor can be connected

Integrated fan

customers like: Max. charging current

customers like: Weight

by SPYRIDON M.

Amazing unit This is the best purchase i have ever made. Very robust made, extreme easy to install, runs cool, charges with no problem. The best thing about this charger is not the bidirectional charging which is a unique feature but the fact that you create a common negative between starter battery and house bank ( in this case a lithium house bank) inside the charger ( it bridges the 2 negatives). This offers very precise charge control and eliminates the need to use a common negative bar bus. Best piece of engineering i've seen so far in marine electrics.

Read all product reviews

Product data

SVB item number 33347
EAN 5060868551170
Manufacturer no. BB1240
Description STERLING - BB1240 bidirectional battery to battery charger 12V / 40 A
Max. charging current 38 A
Output voltage 12 V
Input voltage 9 - 16 V
Device type Battery-to-battery charger
Battery type Lead-Acid, AGM, Gel, Lithium (LifePO4)
Engine running detection Yes
Bi-directional charging Yes
Optional remote display/operation Yes
Temperature sensor can be connected Yes
Integrated fan Yes
Bluetooth No
NMEA2000 No
CAN Bus No
Width 130 mm
Height 163 mm
Depth 56 mm
Weight 0.8 kg

Accessories

STERLING Bidirectional B2B Charger Remote Control

only €119.95

VAT inc., ex-works

Product details

Reverse charging feature
The STERLING BB chargers are able to charge in both directions. Provided there is over 13.2V on the leisure battery (13.5V if lithium) and the starter battery is below 13V the BB shall allow approximately half current (~20A) to flow back to the starter battery up to about 13.4V (float voltage). This allows the starter battery to remain topped up when there is surplus energy in the leisure battery. This feature will NOT drain your domestic battery â€“ it simply takes surplus. Once the alternator / engine turns on or you provide the STERLING BB with an ignition signal the STERLING BB reverts to normal charging of the leisure battery. The reverse charge feature can be disabled, but is on as default.
This is ideal for allowing the starter battery to remain topped up when you are charging your leisure battery.

Insulation
STERLING BB battery-to-battery chargers insulate the 12V starter battery from the 12V leisure battery. This protects the starter battery against accidental discharge and ensures that your engine is always ready to start.

Choosing the right STERLING BB charger
The STERLING BB bidirectional battery-to-battery charger should be rated at around 25-50% of the current rating of your DC-DC converter. This allows the converter to provide the power to run your obligatory loads (steering, lights, stereo, air con etc) and surplus to go in to your 12V auxiliary battery. For example, if your converter is 190A rated, use a STERLING BB1270 - it shall provide ~60/70A to charge. If the full use of the converter is being used by all ancillaries the voltage shall drop across the 12V system and the STERLING BB shall naturally reduce performance and eventually turn off during that episode when there is a high power demand. The STERLING BB shall turn on again when the voltage climbs.

Lithium compatible
Charging lithium batteries will likely exceed the charge rating. If your converter is 200A rated but your lithium battery can only handle up to 100A - the converter will try and provide 200A but the battery(s) BMS will trip out. The benefit of the STERLING BB charger is that it limits the current directly.

Always the right charging voltage
You will get the correct charge voltages at the 12V auxiliary battery. Some DC-DC converters deliver a constant charging voltage of 14.7V, which may be too high for some battery types! With the bidirectional STERLING BB battery to battery charger, you always have the right charging voltage, regardless of whether you are using a lead-acid, AGM or lithium battery.

Automatic start of the charging process
Once your alternator / engine turns on or you provide the STERLING BB with an ignition signal , it starts charging. Alternatively, the integrated vibration sensor can also activate the charging function after two consecutive vibration events. The vibration function makes it possible to install the STERLING BB charger without having to install an ignition signal. This is also an operational method if you have a smart alternator/Euro 6 engine (or younger). Please note the instructions regarding vibration mode in the operating instructions.

Further advantages of the STERLING BB charger

Smart Alternator/Euro 6 compatible
Ignition feed or Vibration Sense modes
6 pre-set battery types
6 self recovering protections
Low temperature trip for Lithium Ion batteries
Quiet thanks to passive ventilation

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Technical Data

Input voltage:	9 - 16 V DC
Continuous output power:	38 at 14.41 V (approx. 550W)
Continuous input current:	42 at 13.68 V (approx. 575W)
Standby power:	5 mA
Efficiency:	95 - 98 %
Protection functions:	Undervoltage protection Input overvoltage protection Output overvoltage protection Overcurrent protection Charge over temperature
Operating temperature:	-20 °C to +60 °C
Cooling method:	Thermostatically controlled
Dimensions:	165 x 130 x 56 mm
Weight:	0.8 kg

Max. charging current

38 A

Bi-directional charging

Optional remote display/operation

Temperature sensor can be connected

Documents

Datasheet

PDF (998,61 KB)

Manual

PDF (3,55 MB)

Systems

Product safety

What other SVB customers have to say

100% real reviews

3 customer reviews

5 (out of 3 ratings)

5 Stars

(3)

4 Stars

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3 Stars

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2 Stars

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1 Stars

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100% recommend SVB

Advantages
Max. charging current (1)
Weight (1)
Connection options (1)
Range of functions (1)
Delivery contents (1)
Price/performance ratio (1)
Mounting/Installation (1)
Max. charging power (1)

by SPYRIDON M.

2/22/2026 Verified purchase Variant: 33347

Amazing unit

This is the best purchase i have ever made. Very robust made, extreme easy to install, runs cool, charges with no problem. The best thing about this charger is not the bidirectional charging which is a unique feature but the fact that you create a common negative between starter battery and house bank ( in this case a lithium house bank) inside the charger ( it bridges the 2 negatives). This offers very precise charge control and eliminates the need to use a common negative bar bus. Best piece of engineering i've seen so far in marine electrics.

Advantages
Max. charging current
Weight
Connection options
Range of functions
Delivery contents
Price/performance ratio
Mounting/Installation
Max. charging power

by Alexander R.

8/14/2025 Verified purchase Variant: 33348

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Very easy to install and operate

The B2B charger is very easy to install!
The device does its job reliably. I particularly like the fact that I can charge my starter motor (lead-acid battery) via the on-board battery (LiFEPo battery) (reverse charge) by connecting it to the mains power.