On a recent shoot I narrowly avoided a serious potential problem when I plugged in an Arri 24v battery into a Panavision Alexa. Thankfully the result this time was that the Alexa simply did not take power from the 24V, however the 1st AC I was with, when I bought up the issue, pointed out that we were lucky the Alexa didn't blow due to a difference in polarity with the batteries.
At the time I didn't get a chance to ask any more detail, but could somebody explain exactly what the issue is here - I'm not that learned about electrics, voltage, amps and so forth. What exactly is going on and, in future what sort of things must I be aware of when mixing different components from different rental houses? Also, are there issues connecting 24v batteries to equipment that should usually accept a 12v battery, or does it simply power it for longer?
Purely for my own interest, is this something that should be obvious to a 2nd AC? It was a multi-camera shoot and a couple of the other 2nd AC who had been assisting didn't realise this either, but it seems fairly important to know given the consequences!
Thanks in advance for the input.