Sterling Battery-Battery Maintainer 12V-12V, 3A

  (7 Reviews)
Price:  £86.24   (£71.87 Exc. VAT)

Product code:  P02157
Brand:  Sterling Power
Voltage  12-12V
Current Rating  3A



4 in stock

The Sterling Battery-Battery Maintainer is a simple, low cost solution to preventing your battery self-discharging and becoming damaged; keeping it in optimum condition and extending service life.

The Maintainer works by allowing some of the charging current supplied to one battery by a 12V DC charging source (e.g. mains charger, alternator, solar, wind) to be diverted to a second battery to keep it maintained.  A typical use for this device would be where you have a leisure/auxiliary battery being charged by a mains charger or solar charger and you wanted to keep a starter battery maintained using some of this power. It can be used with any combination of battery chemistries (lead-acid & lithium for example), providing they are both at a nominal system voltage of 12V DC, and supplies a 3A max. charge current once the source battery has reached 13.3V. When the source battery reduces to 12.8V the unit will go into standby mode.

The Maintainer is simple to install, being fitted in-line between the positive terminals of the two batteries with 10A fuses (recommend by Sterling). It also requires a negative connection that must be 'common' with both batteries.

Its IP65 rating and ignition-protected design make it particularly suitable for use in harsh marine environments.


  • 3A max. trickle charge between two 12V batteries (or banks of batteries)
  • Works with all battery chemistries and combinations
  • LED indicator lights to show charging & battery status
  • Over-temp, over-voltage and reverse-polarity protection
  • Aux battery low-voltage warning
  • Low self-consumption (uses FETs rather than relays)
  • IP65 rating and ignition-protected for marine use

Further information

This device is not intended to be used to 'bulk' charge a heavily depleted battery as it has no multi-stage charge capability and the current is too limited. It is for maintenance charging to support small loads (approx. 0.5A continuous drain) and prevent self-discharge.

  • Compatible battery types: Lead-acid (wet, gel, AGM) & lithium
  • Nominal system voltage of 'source' battery: 12V DC
  • Nominal system voltage of battery being charged: 12V DC
  • Max. trickle charging current: 3A
  • Activation voltage: 13.3V DC
  • De-activation (standby) voltage: 12.8V DC
  • Current self-consumption: <2mA
  • Protection rating: IP65
  • Reverse polarity protection: Yes (via on-board fuses)
  • Over-temperature protection: Yes (unit shuts down at 80°C)
  • Over-voltage protection threshold: 15.5V DC (unit will shut down)
  • Aux battery low voltage warning threshold: 12.6V DC and below
  • Ignition protected: Yes
  • Supplied cable length: 1m
  • Cable cross-section: 3mm² (12 AWG)
  • Overall dims: 140 (L) x 45 (W) x 40 (D) mm

Part Number:  BM12123

Average Rating (7 Reviews):  
Write a Review and share your opinions!

Nice and compact
28 March 2024  | 

Does what it says and works perfectly

Sterling batt maintainer
18 March 2024  | 

Bought this to ensure vehicle battery stays charged from solar panels when parked up for weeks. It was this or the battery master both do the same thing. Have bought Sterling products before so had no issues with quality. Also sterling unit had a higher output. Does exactly what it said it should, been in use for
several weeks now, no issues I'm hoping it's going to be fit and forget.

Battery maintainer
12 November 2023  | 

Quick delivery and good value. Working well so far.


Thank you for the great review

Start battery protection
27 February 2023  | 

Installed on Friday 24 th Feb. Immediate increase in voltage. Probably saved the batter's life, and it will be ready for immediate use when we return.
Love it!


Thank you for the feedback Desiree!

Sterling B2B maintainer
01 August 2022  | 

Bought this unit for our motor caravan to maintain the starter battery's drain while in winter storage via our Victron solar charged leisure bank and so far it's doing a great job.

Sterling Battery-Battery Maintainer
27 February 2022  | 

After taking advice from your tech team purchased this maintainer. Simply easy to fit instructions and does the job. One technical info missing from the instructions is that as soon as dark falls or a grey day the coloured led stop working. This first created a headache and after contacting the tech help it appeared to correct. So if this bit of info could be included I think will help other purchasers.

Prompt delivery as always, quality product.
10 June 2021  | 

Brilliant service as always, Sterling battery to battery maintainer being used to feed back/ maintain started battery via solar. Working perfectly.

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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