\[ a \left (a^2-2 b e^{-a x}\right ) y'(x)+a^2 y''(x)+b^2 e^{-2 a x} y(x)=0 \] ✓ Mathematica : cpu = 0.0346901 (sec), leaf count = 45
\[\left \{\left \{y(x)\to \frac {e^{-\frac {b e^{-a x}}{a^2}-a x} \left (a^2 c_1 e^{a x}-b c_2\right )}{a^2}\right \}\right \}\]
✓ Maple : cpu = 0.053 (sec), leaf count = 40
\[ \left \{ y \left ( x \right ) ={{\rm e}^{-{\frac {{a}^{3}x+2\,b{{\rm e}^{-ax}}}{2\,{a}^{2}}}}} \left ( \sinh \left ( {\frac {ax}{2}} \right ) {\it \_C1}+\cosh \left ( {\frac {ax}{2}} \right ) {\it \_C2} \right ) \right \} \]