BMW R1150GS Auxiliary battery for camping etc. Build & Install

In order to charge phones/tablets and any other devices when camping I have fitted an auxiliary battery to the GS. Luckily my bike is the non-ABS model, so the space where the ABS pump usually goes is more than big enough for a 10Ah battery and charge electronics.

There are two outputs from the additional battery, one is a socket mounted in the side of the fuse cover and the other is to a cigarette lighter socket in the topbox.
You can plug a phone charger in the topbox and lock it away if leaving the bike unattended or whilst riding to keep it dry.

The additional socket on the side of the bike enables a special box I built to plug in, this box has two USB 5V chargers in with a switch mode regulator and a 4W LED light to illuminate your tent.

This all means that you can have as many gadgets and lights running as you like, as the bike will always start from the normal battery in the morning.
There is also a 5mm Bi-Colour LED on the dash, which tells you the state of the battery.

LED Status Indicator
Solid Green - Aux Battery Charged (>12.7V) - engine ON
Solid Red - Charging
Flashing Red once in 5 seconds - Aux or bike battery <12.2V - 25-50% charged
Flashing Green once in 5 seconds - All Healthy - engine OFF

The microcontroller picks up an input from the alternator which ensures the charge relay is only engaged when the engine is running. It then disconnects the battery every 15 minutes and waits for the battery voltage to settle. Once it is settled, the aux battery voltage reading determines if the battery is charged yet. Once it is above 12.7V after this test, the green LED illuminates and the relay stays disengaged.

If the voltage of the aux battery then drops below 12.7V, the relay kicks back in and it starts all over again.

After a year, I decided to add some extras on and tidy up the wiring.
One particular problem was the fuseholders were positioned under the fuel tank, so if a fuse blows it means taking the tank off. This only takes five minutes, but is a pain when out and about.

I brought a 6 way blade fuseholder for £4 and made a bracket to bolt it to, this then nicely sits under the seat. 

As well as the new fuse box, I decided to add a 50AMP anderson connector so that we can jump the bikes, plug them together or use a set or crocodile jump leads I keep in the topbox. The cable is 4AWG which is rated to probably 135Amps and absolutely ample.

The last trip ended up with us in the middle of nowhere with a flat battery and jump starting Matt's bike from mine with some fence wire we found. We will be better prepared next time!!

I have added some extras to the setup in the form of a new cigarette socket in the top box with an LED sidelight I had kicking around:

I also added a cigarette lighter socket in the right pannier, my plan is to buy a 12V cooler bag but my thoughts are that it will not work well without any ventilation in the pannier:

I also added another LED light to the side of the bike for camping and breakdowns etc. at night. This is powered from the auxiliary battery so you can leave it on all night and still start the bike in the morning. I have put a small switch just under the seat to turn it on and off: