Electrical calculation
If this is a Lithium battery my answer does not apply.

The battery capacity is 1600mAh.

The solar cell can supply 42mA.

\$t=\frac{1600mAh}{42mA} =&gt; 38h\$

This is a very rough estimate, and can be used for both charge and discharge times.

EDIT

With LiPo batteries, you don't want to exceed the battery cell voltage, 3.7V in your case.  When the batteries are near full charge, and not pulling much current from the solar cells, then the solar cells you have selected will attempt to keep pushing current into the battery by increase their voltage towards 6.2V.  That's double the battery cell voltage and will most certainly damage the battery.  You would need a battery charge controller to handle this.
Google "lipo charge controller" and you'll see lots of options.

The mechanism described also happens with Pb, NiCd and NiMH but they are more tolerant of it.  Lithium batteries are not.  However any system designed to last will want a charge controller designed for the battery chemistry in use.