Batteries parellel

[tr6scott]

Ok, can someone enlighten me with some data on what we should see/best practices/avoid in the future?

When we do parades, we use a y battery connector, so that we can keep the bot alive as we hot swap batteries. We do not run the robot while in this parallel connection, it is done to keep the cRio alive, and able to continue on without a reboot.

Typical scenario:
Battery starts off at 13.5v and we drive, shoot, pick up balls with our rebound rumble bot. Typically about 10 mins into the parade, battery voltage is around 10v and things get wonky, (that is the technical term, that is really only understood by the students and drivers.) We stop the robot, plug in a 13.5V battery into the secondary connector of the y, unplug the 10v battery, and continue on with the parade. This swap usually takes about 30 seconds total. While we are doing the swap, there is little power being used on the bot, no motors running, just keeping the electronics alive.

We do this 2-3 times in a typical parade that lasts about 30 mins in Oxford. By the end of the parade the motors are hot, and ready for a cool down.

We have done this 2-3 times a year, for the last two years.

Am I risking the lives of the students, and the entire Oxford community?
Should the Y connector be redesigned with some diodes?
Should the Y connector have a some lower amp protection say 40amp automotive fuse for some catastrophic failure of the "keep alive" leg, and only use that leg to keep the bot alive? ie, time for a battery swap, plug in "keep alive" battery into the 40amp protected connector, pull 10v battery, replace with 13.5 volt battery, unplug keep alive battery. A little more cumbersome, but is it significantly safer?

Data please?