What year is your bike?
Post-'01 bikes do a better job of maintaining voltage throughout the RPM range than the early bikes but don't have kickstarters. If the load exceeds the charging system's ability to replenish the battery you could wind up afoot, particularly after short trips or low RPM riding.
A small voltmeter would help you monitor battery voltage as you ride. 24W is a substantial load, but you could switch it on and off according to the volt meter if it affected charging.
The voltmeter won't tell you how many watts are available. It will only tell you when your voltage is dropping.
The gloves should draw less (or at least less often) at the lower settings and at full RPM the system may fully support them. The only way to know is to try.
The voltmeter is just my .02 due to the absence of the kickstarter on the late models.
If you live in the u.s. I have some for sale in the classifieds.
It's a 2006. If I ride with a voltmeter attached will it tell me how much extra watts I have, before I purchase the gloves and install them?
I believe the temperature controller has 5 settings and an on/off. Would I be safe to assume that the listed power usage on the gloves, the 24 watt draw, would be at max settings or do you think it would be consistent?
I live in Manitoba, Canada. Do you have the ones sold by Powerlet? If so, did you use them with the TW and how'd they work out?
They are sedici brand sold by cycle gear. I have used them with the tw but have only had them maxxed out to let them heat up. Didn't notice any dimming or anything that led me to believe they were putting a strain on my 2010's system. I also was charging my phone at the same time. They are very comfortable and I kept turning them from the lowest setting to off because they would get too warm! That was riding in 38° weather. I'll ship them to you for $110.