High voltage means nothing if the power source can't deliver the current. You could use a transformer to step up a AAA battery to a billion volts and it wouldn't do anything because a battery can't actually push out 1B/[your body's resistance] amps.

With low voltage battery circuits the main thing you have to be wary of is capacitors because those can push out a lot more current than the battery itself. Usually you can judge how much a capacitor would hurt if you touched it based on its size. If you have a device with 20 batteries charging a baseball sized capacitor, be very cautious (like the DIY gauss guns/rail guns you see on youtube). Even a thimble sized capacitor will jolt you surprisingly hard. One time I touched the charged capacitor of a disposable camera and the discharge gave me quite the zing.