What you want isn't really different than what many have on their bikes...

Why not get an optimate plug for your battery and give it an overnight charge every week if you feel you're draining it a short commute and lots of accessories. Its the same issue sports bikes have with their small batteries and alarms etc.

If you want to get away and do some long days and fear that you're accessories are too much for your generator, then by far the easiest and more relevant (and cheaper) option would be a higher output generator.

You don't need to buy a big gun for a knife fight !!

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Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

Standard set-up on the VW minibusses. My Type 4 have it set-up incorrectly though... the power to the rear-lift (http://www.u-lift.se/en/) it taken from the starting battery and not from the auxilliary battery... before I knew this... jumper-cables were used a lot

There are a few options how to set-up dual batteries.
- an electronic relay that opens the circuit once the ignition is turen-on (like on the vw)
- a switch that you operate manually (belive it to be common on small boats)
- fully in parrallell (standard on older VW campers)
- not connected, simply carried along.

My recommendation is:
Batteriväljare, 1-2-1+2 - Biltema
Page 4 - in English:
http://www.biltema.se/Documents/manu.../25877_man.pdf

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Drive Safely,
Albert

A VSR is the a good method of isolating and charging 2 batts. It senses when the engine start battery reaches a certain voltage and then parallels it with the other battery. If the voltage drops it seperates the batteries and only charges the start battery.
A battery isolater diode set up is not so good as you suffer a voltage drop accross it which is inefficient.
Durite make an economical VSR
0-727-33 12V Durite voltage sensitive relay for charge splitting - TheToolBoxShop.com

I'd start by calculating the actual power usage. My K100 actually makes enough power to run two heated jackets, a pair of fog lights, a rear fog, GPS and charge my phone. Only at temperatures below freezing goes the expected system capacity drop below what I can actually use. I'd wonder what you might be running on a solo bike that would actually used the power?

As I've got the space and they are cheaper, I run a car battery in the chair. I also have a caravan smart relay that I can link to a second leisure battery. This facility is there so I could run a fridge if I really wanted to and in cold places have a second battery I can take off/keep in my sleeping bag/jump the bike off. The whole lot came from a caravan accessory website.

Andy

Have you thought about how much extra weight you're adding? And the extra load on your alternator when it has to charge two batteries?

Why not fit a battery saver between the battery and the accessories - It will cut them off once the voltage gets to a pre-set point, preventing any further discharge...

I've ask among my contacts and they recommend:
Relé / Isolator

The Ladac (Ladix) system is said to be better since will not open the circuit to the second battery before the starterbattery is fully charged.

I've thought about this for ages, i.e. since The Crystal Rally 1994. I would have needed two batteries at that time. Looking into the options back then I could not find any workable solution. On the R80 1984 I could have installed one 30Ah or two 14Ah, since the Bosch startermotor kind of requires a minimum of 19A at summer and 24Ah at around freezing, I crept to the cross... and accepted that a solo-bike have not enough space for a second large battery. The 28Ah were ok when temps stayed above -15'C but even at so moderate temps as -20'C they simply were not powerfull enough. At www.sga-ab.se they recommended that I should test Banner 53030, 30Ah, - these 2Ah tipped the scale in my favour.

Since 1995 I'm running a Valeo-starter motor. With this startermotor I think a 14Ah would do nicely however .
I stay with the Banner 30Ah, but I have an Odyssey PC-625 for my summerbike, and this battery have so far proven to be far superior to the Banner, Yuasa and BWM batteries that I have had during >30 years of driving bikes and cars.

Point:
- space is a limiting factor on a bike
- if one uses electrical equippment like car-radio with amplifier, lights, etc it it far better to have two smaller batteries than one large; ensuring that the starterbattery will not be depleated "by accident".
- best option is to have a battery switch that is fully electronic, that primarilly fills/charges the starterbattery, even though a simple 40A relay will also work ok (my buss have had this set-up from factory in 1995).

How far have your plans developed Brama?
Which batteries have you considered / can be installed?
Installation solutions? Pannier, pillion seat, top-box, ???

__________________
Drive Safely,
Albert

Thanks for the feedback...I will pursue it further and post my progress
Cheers

I like the idea of a dual battery setup not (in my case) for the additional grunt it gives you for running accessories - basically everything you run should < alternator output anyway! - but simply from a spare battery standpoint. Two batteries, with an isolating switch (either manual or automatic) between them gives you spare battery should one fail and a spare battery should you have left something on and drained the battery.

My thoughts would be to fit to 2, much smaller, lighter LiFe (Shorai style) batteries with a switch between them. The smaller size and weight should make up for the fact that there are 2 of them. Ideal if you can find 2 batteries that are the same size as the single original battery and fit both of them into the original spot.

You aint gonna find much bigger than the 720 watt unit on the adventure mate. Its already the highest output unit I have ever heard of on a bike

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Here we go again...

Please, do not confuse alternator out-put with battery capacity.

I run a 70A Bosch alternator on my winter-beemer, that is 980W at 14V. I run it at 14V at summer and 14.8V at winter, which results in 1036W then...
I have a 90A that I will install on my summer-bike. That is 1260W at 14V.

I have tested large alternators to any since battery between 14Ah to 100Ah - the battery gets charged, not cooked. No problem.

I have also tested the opposite situation, the beemer stock alternator of 20A (or so they claim...).
It will charge any battery from xAh to 100Ah - it simply takes more time to do it. However, the original beemer charging system have some flaws that need to be adressed, what ever battery that one is using, to optimize charging.

In my VW buss I'm running a 80Ah startbattery and a 80Ah backup. The alternator is a 120A (1680W at 14V). On the older vans one had a 55A alternator and dual 70Ah batteries.


The out-put of the alternator will only tell how much load one can put on it, not how it charges the battery...
If one want more gadgets consuming electric power, one will have to install a stronger alternator. That, can be a bit tricky though...

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Drive Safely,
Albert