first look at the change between t=0 and t=1
difference between 0V and 9.8V is 9.8V
so between t=0 and t=1 the ΔV=9.8*0.63
since the starting value of V (at t=0) was 0 the value at t=1 is
0+(9.8*0.63) V
so at t=1 V=6.2V
next look at the change between t=1 and t=2
difference between 6.2V and 9.8V is 3.6V
so between t=1 and t=2 the ΔV=3.6*0.63
since the starting value was 6.2V at (t=1) the value at t=2 is
6.2+(3.6*0.63) V
V=8.5V
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alternate method
The more 'classy' way of doing it is
V=Vbatt(1-e-t/RC)... but I don't think you get given this on your formula book
I think of t/RC as being 'number of time constants'
fwiw 1-e-1 is 0.63 which is of course where the 63% per time constant comes from.