Cars and bikes all of them, just as an easy first step, I've got a set of multimeter leads with alligator clips [I often have to monitor three multimeters at once, probes are worse than useless unless you got eight hands] that I attach to the battery, set the meter to DC Volts [first] and just watch the voltage before I start, while cranking, while changing rpm a bit, while adding loads, whatever they are - lights, in your case heated accessories so on. You'll see if any of your gear "browns down" for lack of a better term [causes your voltage to drop] your power plant.
Here's how my 13 reads, and although it's 14.2 VDC immediately after starting, I think that will settle closer to 13 after a bit, but others will know these values for your ST better.
My own voltage measurements from earlier this summer between rides, bike started cold after about one day.
12.56 VDC Static - Battery appears well charged; below I think 12.4 you're already behind.
11.63 VDC Key On / Post Fuel Pump Prime / Head Light and Instrument Cluster On. - Should only slowly drop if left in this state for a few seconds.
10.30 VDC during the cranking phase fairly steady, but brief bike starts pretty quick. - If you're voltage droops much more than this, you've either got a weak or inadequate battery, or you're drawing excessive starting current.
14.20 VDC or something close to that once the bike runs. - Means your alternator is developing a high enough voltage to run your gear and recharge your battery.
