you should be able to run a heated vest and grips together, but not too much more than that. You definitely should get one of those cheap voltmeters, though. You don't want to kill your battery or get stuck somewhere. I've got the ability to switch off one headlight, via the Eastern Beaver headlight relay with cutoff switch. That allows me to run grips, jacket, pants, and gps. I also replaced parking and license plate bulbs with leds. I never run the gear on high. Never really need to, as medium seems plenty.
2014 DL650 (sold)