Words by Ramsay Beacham
Photography by Lachlan Payne

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In most cases, these are activated by your vehicle’s ignition to effectively join your two batteries as soon as you turn the key. Of course, the downside is that your potentially flattened auxiliary battery will drag down your main battery, which will give you a half-charged combination.

This might be enough to start a two-stroke Suzuki that is low on compression, but it would be about as useful as an ashtray on a motorbike in anything else. By incorporating a manual override switch, a la driving-lights, it is possible to override this system for cranking with a dead-flat auxiliary.

Route the red ‘live’ wire around from one battery to the other via the isolator with the provided zip-ties. Avoid hot and/or sharp obstacles along the way	Mount either your starter solenoid or isolator away from any heat sources. The Baintech VCR is as simple as it gets – one wire for the crank, one wire for the auxiliary, and one goes to earth
At just $1.75, I thought I’d give these felt terminal post washers a go. They are supposed to stop the build-up of gunk on your battery. Only time will tell	Use a multimeter to check the operation of your new dual-battery set-up. It should only connect the two batteries when the main-battery voltage rises above 12.7V

Another consideration worthy of a second thought is that manual switches and solenoids do have the potential to create voltage spikes. They are not recommended for use in vehicles with EFI motors, which can be sensitive to this.

If you don’t like my fitting instructions, why not try the official ‘fit and forget’ ones. Apparently the six-pack is to help you forget how dodgy your DIY wiring is

This handy unit comes in at $169

The next step in technology is a voltage-controlled battery-management system. By cutting in and out at pre-set voltages, they give charging priority to the main cranking battery and ensure starting duties are taken care of only by the crank. These systems are also suitable for modern EFI engines and are the best foolproof systems available today.

An automatic dual-battery system install is one of the easiest DIY projects I’ve attempted. The wiring is as simple as it gets, and there’s no crawling around under the dash looking for live wires and the likes. A full install in a typical engine bay would take no longer than half an arvo and costs less than $400 including a battery cradle, full-sized battery and automatic isolator.

Baintech VCR

Bainbridge Technologies offer an entry-level VCR (Voltage Control Relay) known as the Baintech unit (pictured right). It’s one of the smallest, simplest, cheapest and most effective units on the market.

For 12V systems, the Baintech unit will only connect the cranking and auxiliary batteries after the cranking battery has reached a pre-set 13.4V. It will disconnect after the vehicle is turned off or when the cranking battery drops below 12.7V.

In doing this, the Baintech system ensures that the main starting battery is fully charged before connecting your second battery for replenishment.

Baintech units are self-protected from reverse-battery connection and alternator load dumps of up to 80V over 120milli seconds, not to mention being waterproof.

At just $169 for the 12V model, the Baintech VCR offers excellent value for money when it comes to voltage-controlled relays.

Visit the website www.baintech.com.au to find out more on this and other products.

Costs

The costs involved in a dual-battery set-up vary greatly depending on the hardware used. A battery tray from Supercheap Auto including nuts, bolts and clamps can cost as little as $40. A means of isolating your second battery is as little as $13 for a starter-motor solenoid through to around $170 for the ‘smart’ Baintech unit we used.

You can get batteries from a little as $50, but the sky is the limit from there on out. Your battery choice will most likely reflect your budget. Deep-cycle, gel-cell, yellow-top, blue-top, red-top and every other rainbow-coloured top you can think of are just a portion of the batteries available on the market today.