Dual Battery Question

[drwalker57]

2007 R1200RT-P: Has 2 batteries, Main and Aux. Each battery has a two-pin cable & plug attached directly to the battery terminals. The main cable & plug is snap tied to the frame. The aux battery cable & plug sits in the top of the sun-glass sized compartment directly above the aux battery and accessible from the small door just right of the steering compartment.
It appears that these two cables could be plugged into each other. Is that how the batteries get placed in series?
Wiring diagrams I've seen suggest the batteries are in series by default. Anybody know for sure?
The main battery is a little weak and I thought it would be good to have access to the aux battery if I needed extra boost to start.
Sorry... I'm a complete novice.
Thanks much,

[David.]

Having done some "Google" research, my educated guess would be that the aux. battery cable & plug is for supplementary charging from an external source,
i.e. a battery charger.



If the main battery is weak, what condition is the aux. battery in, a voltage check would be good. Without getting too complicated, from what I've read elsewhere, both batteries are charged from the bike when it's running. The main battery has priority, once it is fully charged, current is then diverted to the aux. battery.

When jump starting, an additional battery or starter pack is connected to the main battery using leads connected in parallel, +ve to +ve & -ve to -ve.
It might not be a good idea to have the aux. & main batteries permanently hardwired together, (the split charging from the bike would be by-passed). The aux. battery was never intended to support the main battery for starting the bike. On an RT-P the aux. battery is there to support additional electrical equipment whilst the bike is not running. Hence, it can become rundown whilst the main battery is protected for starting the bike. Plus, the current carrying capacity of the supplementary battery charging cable will be significantly less than that of a jump lead or the main battery earth & positive cables.

If the main battery is suspect, I'd be looking to change it, after first checking that the bike battery charging system is working ok.

The main & aux. batteries are the same, if the aux. battery is in better condition than the main battery, how about switching them around.
The aux. battery itself has no bearing on the starting circuit of the bike.

[gogs01]

Whatever you do, I would advise never to connect these batteries in series (+ve to -ve, -ve to +ve).  This would give 24 volts and would cause havoc.
If you connect them in parallel (+ve to +ve, -ve to -ve) then you effectively have one large 12v battery.  Whether this will improve the starting of your bike depends on a few different factors but, in theory it could.  If the wiring you use is sized for an external charger, there is the potential for the wiring to overheat or burn if the starting current for the bike goes through it, so perhaps the best advice is to consult an auto electrician.
Good luck.

[drwalker57]

The main & aux. batteries are the same, if the aux. battery is in better condition than the main battery, how about switching them around.
The aux. battery itself has no bearing on the starting circuit of the bike.

Great idea, both batteries seem to take and hold a charge, but the Aux is stronger. Haven't actually tried to start the bike yet, working through a fuel leak issue.

Thanks for the insight.

[exportman]

Hi


If connected in parallel you may find the weaker battery drains the better one  so keeping them isolated as the system is designed would be preferable.

[heathy65]

remove the starter motor and have it checked by a reputable Auto electrician. you may find thats where the problem is.