Really?

What is the shorted time when flipping the switch?Â* What's the voltage
difference between the two batteries?Â* What's the total circuit
resistance, including the internal resistance of the batteries?Â*
Theoretical math and practical application do not always agree.Â* It
might be fun to set up such a demonstration and use your o'scope to
measure that current and it's time duration.Â* Compare that to the "blow
time" of any fuses.

Seriously, I've done it for years without any problems, but I recognize
that past performance is no guarantee of future results. I'd be curious
about the results and you have the equipment to do it.

On 4/16/2020 12:21 AM, 2G wrote:
On Wednesday, April 15, 2020 at 6:18:08 AM UTC-7, wrote:
While I am reading these posts with interest, I confess to being an electrical illiterate. I just use two batteries, each with a fuse, and two switches. When switching, I turn on #2 before turning off #1.

If these circuits with diodes, resistors, make-before-break switches and so on are superior, please explain why, and if the case is compelling, a circuit diagram would be appreciated so that I might take advantage of the information.

After all, in aviation "R & D" actually stands for "Ripoff and Duplicate."
A make-before-break is also called a "shorting" switch. If you use such a switch you WILL short the two batteries together, which could result in a large current flow from the battery with the higher voltage to the battery with the lower voltage. This large current could blow your protection fuse(s). This is especially the case if you have two separate switches.

--
Dan, 5J