My rational is that people put 12V batteries in series ALL THE TIME (RV power, solar systems, electric fork lifts, goldf carts) and I can guarantee they are not all the same current and those do NOT blow up.
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Actually hooking the 12v rails together is like hooking batteries in parallel - which you can usually get away with as long as one of them does not short out when it fails. Also, the internal resistance in a battery to current flowing backwards through it provides some additional protection. If you start mixing types and brands of batteries and/or old ones with new ones you are more likely to see the stronger batteries discharging themselves through the weaker ones...
RM
PS - hooking power supplies in series would be even worse. If both supplies are "grounded", you would be tying one of the power supply outputs directly to ground!!