Hello, what is the best way to keep your battery charged while the bike is outdoors and unlikely to be used for the next couple of months? I was thinking of disconnecting it and a trickle charger, however, is there anything else short of running an outdoor mains cable from the shed to an Optimiser?
You can connect it to a solar panel and attach that to your cover. How much sun and how long it will last, that depends…
Solar panels will work. I left a car parked up for months on end, often three or four months at a stretch. Solar charger on the rear parcel shelf kept the battery in good condition. That was over ten years ago, I imagine the tech has got better since then.
Solar panel is a good option. The battery needs to be in good condition and fully charged for them to work effectively. They are also easy to steal if the bike is parked on the street. If it’s a 2 month break I’d suggest hauling the battery out and connecting it to an optimising charger in your house. It’s important that the room is well ventilated.
If I knew it was going to be parked up long term, I’d probably take the battery off and bring it indoors for charging. Also less likely to get stolen.
I meant until someone nicks it if it’s on the street 
That is true. On the street it wouldn’t last 24 hours.
Battery maintenance is a numbers game. What you need, if in fact you need anything, depends on the battery’s stand by current drain. My trusty steed has virtually zero stand by current drain once the ECU enters sleep mode which is after 24 hours of being stationary. It can and has been left for many extended periods and having only been exercised on four or five occasions last year it starts on the button first time every time with no battery maintenance other than a monthly check on voltage. The voltage never drops any lower than 12.6v and that’s on 4+ year old, cheap as chips, old school technology lead/acid battery.
With a bike on the street I’d expect it’ll have an alarm which will drain current. Also if you have any accessories (heated grips, USB sockets, 5v regulators etc) wired directly to the battery these will drain current too, despite what some accessory manufacturers claim. So get yourself a multimeter, check the stand by current and act according.
A solar charger will need to replace the stand by current + 10% to keep the battery in a state of charge. Take into account here the hours of daylight and the figures aren’t good. All those claiming solar panels worked for them need to also state the numbers (stand by current drain vs solar panel output) so a like for like comparison can be made to deermine if a solar panel solution will work for you!
Optimate type chargers are best if you have high levels of stand by current drain because they work the battery by a constant charge and discharge process.
Your best option, assuming the bike is alarmed, may be to have two batteries, check the voltage monthly and swap batteries as required or, if you don’t have an alarm simple remove the battery altogether. Remembering even with the battery removed you’ll need to regularly check the voltage.
Thanks all, the bikes in the garden, I have a solar panel, I will dig it out and get it charged up.