I’d practice on B & C.
B is a 6 cell 3s2p pack (3 series 2 parallel), which means that the cells are, at best, ~2,200 mAh, and generally, those generic packs.
I don’t have experience with Dell packs. The Acer packs I’ve opened have taken some effort. The HP pack I opened was a cinch, and the Asus pack was somewhere in between. I’d suggest going slow.
To start Try peeling off any heavy plastic labels to see if they reveal anything that makes the pack easier to get open. If that doesn’t give any clues, I’d suggest eyeballing the pack from many angles to try and get a sense of how the cells are arranged in it. I’ve had luck using multiple slow, gentle passes with a hacksaw blade (removed from the saw) to scrape through the plastic above a “valley” between two parallel rows of cells on opposite sides of the case, then I use the blade to cut through the ends to connect the channels. From here, I work the two halves of the case apart.
You can also try to work on the original seams of the case, but these have the downside of generally being flush against the side of 1/2 to 1/3rd of the cells), so there is more chance of gouging the wrapper, or denting the metal jacket. This technique is a little slow, but using it, I’ve avoided damaging the cells or the wrappers.
Safe removal of the batteries takes a bit of finesse. They are often secured with glue and/or ridges on the case. A stiff thin piece of plastic slipped between the case and the cells can be useful for teasing them loose.
Once you have them free of the case, take some wirecutters to cut them free of the circuit board. I cut as close to the circuit board as possible. To get the tabs off, I find a free edge and get pliers under it, working it as close to the welds as possible, then I twist to sort of wrap the metal strip over the top of the plier, with the goal of applying force perpendicular to the base of the battery. Generally the welds tear free of the metal conductor strips, but this approach minimizes the amount of metal left behind on the battery.
Again, go slow, try not to force things, particularly the cells themselves. If something isn’t working, try a different approach. Be careful about shorting out the whole pack or cells with metal tools. I think the only way to get mechanically inclined is to take things apart (and put them back together) and pay attention as you go.
I’m sure others have good advice too. Best of luck.