Your sender is hammering your receiver with a steady of of "Nothing happening here" messages. Might I kindly suggest that it "Shut Up!".
The sender should only speak up if it has something to say. A, C, E, and G are useful things to send. B, D, F, and H are useless.
Might I also suggest that the compound if statements are difficult to follow. Rearrange them to use nested if statements, instead.
if(variable == 'A')
{
if(FReedSw == LOW && FPrevReedSw == LOW)
{
}
}
All the stuff that should happen when an A is received should go in this if block.
The saved times get reset even when the duration is less than the interval of interest. Why is that?
Printing to an LCD takes time. Perhaps you ought not be printing on EVERY pass through loop(). Battery voltage doesn't change that often.
Since you are repositioning the cursor, writing the constant stuff every pass seems unnecessary.