Aftermarket seat heaters

I am considering adding a set of seat heaters to my 99 Silverado and am wondering where my truck didn't come stock with them if the alternator is heavy enough to power everything.I had to replace the serpentine belt a couple of years ago and found out that I needed the narrower of 2 belts offered for my truck so that leads me to believe there is a higher output alternator with a wider pulley available as well.Heated seats is the only interior option that this is not equipped with from the factory and having leather seats in this climate in the winter is COLD.Obviously the only time these will be used the most is in the winter when there is added draw from the heater and at times the rear defrost too so I don't want to get into a situation where I'll be experiencing battery or charging issues.I don't know right off what the amperage of the alternator is and really don't want to replace it as it is not very old either so will I be ok with adding seat heaters or am I asking for problems?The kit I'm looking at is from heatedseatkits.com and supposedly comes with everything needed but I have yet to contact them to ask the same question regarding the alternator,I'd like an unbiased answer.

my 2000 LT uses 66amps when all equiptment is on ,,,the a/c uses a lot of power..

the seat heaters I'm guessing use about 50watts of power..that would be 4-5amps...not too much to cause a problem..

the rear /window heaters are what suck up a lot of power..

you most likely have the 105amp...

use a trickle charger permently mounted it the vehicle. whenever its very cold out ,,this will keep the battery warm and when doing short trips the warm battery will rapidly charge..cold batteries don't charge..