Being shocked by 120VAC is severely different than being shocked by 120VDC! The AC tries to paralyze you, but DC just burns it's way through. You do not wnat to come in contact with 120VDC (or pretty much anything above about 36V especially if you are damp or sweaty.)
Even 12V can deliver a good burn if you are sweaty and get between the posts.
36 and higher is just dangerous!
Another thing to consider is that when you have a 120VAC circuit, like the one in your house or shop, it has likely a 15 or 20A fuse or circuit breaker. So, if you inadvertently get the wires crossed, you'll see a flash and the breaker will trip.
Strings of batteries are a different story. . . Unless you put a fuse in between every single battery (redundant and not really necessary) then the more batteries in your string, the higher the possibility of welding your tools and equipment to the battery posts or wiring. If there are no fuses in between the batteries, and let's say you have a 48 volt string and you are on the last one connecting them up. Now, these are 220amp-hour batteries, at 6 volts each. Now, you have 220amp-hours at 48V. Under short circuit conditions (dropped wrench ot etc.) there may potentially be thousands of immediate amps available current. You'll get HURT in other words.
Have Zen-like concentration and serious respect for the DC circuits.
NEVER, EVER attempt to use AC (household or otherwise) circuit breakers with DC circuits. Especially on voltages above about 24 or 36 max. They trip differently and when an AC breaker trips on a high-current circuit running on DC there is a nice little blue flame that could burn your whole operation down to a smoldering mass of CuAlFePbNi.
Don't let this scare you, just respect it and be diligent to use the right stuff in the right ways and you'll be fine. . .
Doug
