Part 1: Jessie Raspbian.
 
Finally got a chance to update and upgrade Jessie on my R-Pi's the other day (on 4/19/16). The issues I had was some strangeness with the upgrade, as it was done on the Raspberry Pi 2 (R-Pi2) on a 2600am battery as I did not have my cellphone power pack with me. Though an update was done to it a few days before, the upgrade would not take, stating that there was nothing to upgrade. For the hell of it, I told the R-Pi2 to update the OS. strangely, it updated again. Then I told it to upgrade. It upgraded the OS files, taking about 40 minutes to do so.
 
But at the time I was having battery problems. The other day (4/18) I charged up my batteries to full. But two of the batteries acted as if they were low. The third battery acted as if it was also low but strong enough to power the R-Pi2. This got me worried as to whether or not the upgrade took. So upon completing the upgrade, I restarted the R-Pi2.
 
At first, the booting process started to go by quickly. Then it started to list errors and kernel panics before stopping in a 1/2 text 1/2 graphic mode screen. I disconnected the battery and plugged it back in, hoping it would fix itself or show itself as a dying battery; which boots up partially and then reboots. This time it look a long time for it to boot, comparatively speaking over three minutes. It was doing a lot of things during this boot process, including accessing the network. But it eventually booted to a Graphical Desktop screen. To see if this would happen again, I rebooted the R-Pi2 again. This time it took less than 10 seconds to boot!
 
I verified it again with another reboot, and it started up in less then 10 seconds again! But the test is to see if it can boot on the other R-Pis. It would be awful if the OS on the SD became a single system Os again.
 
I switched the SD Card to my Model B+ to test it. It started to boot and then crashed with a major Kernel Panic error. Again, I thought this was battery issues I was having before; but the Model B+ takes less power than the R-Pi2. Rebooting caused it to take a long time for it to boot like on the R-i2 before, and then it went into the Graphical Desktop. I rebooted the model B+ and then it booted up quickly.
 
And there I left it without further testing.
 
Today (4/21/16), I did the full test on this one SD Card. First I booted it from the R-Pi2, followed by the Model B+ and then the Model B. This time the R-Pi2 booted up in about 5 seconds! In short, it was fast! and this is a Class 4 SD Card which is slow! Switching over to the Model B+, it took a bit longer as System File Pointers needed to sort themselves out, but it took a bit more than 10 seconds! Rebooting it caused it to boot up in less then 10 seconds, but when the R-Pi switches from Text Mode to Graphical Mode, it takes a few seconds. This does not happen on the R-Pi2. If it were not for this screen mode switching delay, it would boot up faster. The same thing happens with the Model B, the boot process between the two systems, the Model B and Model B+, are nearly identical in every way.
 
So it passes the test! I can continue to boot the SD on any R-Pi system I want. This is a major breakthrough!
 
The only system I did not test this on is the Model A and A+. Though the unupdated/unupgraded Wheezy SD I have boots on the Model A, it is only 256MB of RAM. The OS should run it, and perhaps Libre office too, but considering the limitations of the Model A and Model A+ Internet Access would be difficult at best. When I have time I will test at least the Wheezy SDs to include the Model A and Model A+. In theory the Raspberry Pi Zero (R-Pi:0) should work as well as a Model B and Model B+ because of the same amount of RAM they have - 512MB. But like the Model A and Model A+, the lack of network ports and USB Ports makes internet access difficult on it, though it is still doable. Future tests will include the R-Pi:0 as well as the Model A and Model A+.
 
End of Part 1...