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.

> High voltage means nothing if the power source can't deliver the current

It can still be dangerous though, it can trickle charge an output capacitance which will deliver the current to hurt you. A small battery only charges it more slowly, the end result is a function only of voltage (assuming the battery has sufficient capacity to completely charge the capacitance).