I've seen like four people already post this season that they can't be arsed to winterize their bike, but it's okay because they'll just start it a few times a month/week to keep the battery charged. This is ineffective at best and destructive at worst, for the following reasons.
1. It doesn't actually charge the battery!
The electrical system of your average motorcycle is pretty modest. Usually, simply idling the bike will not do anything to charge the battery, at all. If you have a voltmeter, you can see this for yourself by checking voltage at the battery terminals with your bike idling, and then seeing the difference when you give it just a little gas. Some bikes will not even idle without a battery. On the other hand, starting the bike is the hardest thing the battery has to do. If you've ever had a problem with your bike that made it impossible to start (e.g. bad coil) then you may have noticed the battery runs flat pretty quick, after only a handful of start attempts. For a bike to actually charge its own battery, it usually has to be ridden for 10-15 minutes (made up number) after a start.
2. Starting a motor is the worst thing you can do to it
Of course these machines are made to be used, but you have to keep in mind that the lubrication system is not working 100% until the motor is fully warmed up. When you start a cold motor, first it has to build up oil pressure, which may take a few seconds (watch the oil pressure light if your bike is equipped with one). Until then, moving parts that have not been reach by pressurized oil are skating by on oil residue. Pretty much all bearing wear in a modern motor occurs while starting it. Then, even after the oil pump has built up maximum pressure, the farther reaches of the system are not seeing their maximum pressure - cold oil does not flow well, and "warm" oil will quickly get cooled down by parts of the motor that haven't heated up yet. Also, keep in mind that you're starting it in winter - the bike is gonna take a lot longer to heat up than when it would just be idling in your driveway in warm weather... and cranking a motor in the freezing cold is a lot more stressful on the starter, due to the oil thickening, and your cold battery being able to deliver less power.
3. Condensation
You know how cars in winter have visible water vapour coming out their tailpipes? Of course your bike does that too, but if you start the bike up and it never fully warms up, then you've just covered the interior of your exhaust system with condensation. This is a bigger deal for some exhaust systems than others - maybe you have a VFR with an expensive, plain steel collector that you have now just accelerated the process of it rotting out. If your run your motor briefly enough, you can get condensation inside the cylinders too! Ever heard of stuck piston rings?
4. Don't do it
Repeatedly starting your bike is probably better at killing your battery than charging it. Actually, one good thing about the cold weather is that it decreases the self-discharge rate of lead acid batteries. That means a better idea (if you don't want to buy a float charger/"battery tender") is to just yank the battery out of the bike and put it beside it (in case of key-off power draw from electrical faults, accessories, ECUs)... or barring that, just leaving it in the bike and not touching after a good ride.
Regularly starting your bike in winter is bad
