How to "Hold" variables assigned value inside DSolve?

Consider the following ODE:

a = 0.8; b = 8;
v = DSolveValue[{
   u[x] == a*(b* u'[x] + u''[x]),
   u[4.925] == 4,
   u'[4.925] == 0.625
   }, u[x], x]

which gives the error message

DSolveValue: For some branches of the general solution, the given boundary 
conditions lead to an empty solution

However the following totally work:

a = 0.8; b = 8;
v = DSolveValue[{
    u[x] == c*(d* u'[x] + u''[x]),
    u[4.925] == 4,
    u'[4.925] == 0.625
    }, u[x], x] /. {c -> a, d -> b}

But this is ugly.
I could use Block, but all these are inside Module, and using Block inside Module gives warnings like this:

a occurs twice in a nested scoping construct in a way that is likely to be an error

What is the best way to solve this?

a = 8/10; b = 8;
v = DSolveValue[{u[x] == a*(b*u'[x] + u''[x]), u[4925/1000] == 4, 
    u'[4925/1000] == 625/1000}, u[x], x] // N
(*
-0.000851416 (0.780974 2.71828^(40.9101 - 8.15331 x) - 
   2208.78 2.71828^(0.153312 x))
*)