Hallo Sachin,

charging a lead-acid battery should be done by the help of a constant voltage source. If the battery is all the time connected to charger, and no timed charging is provided, charge voltage must be kept under control very carefully. This is especially valid, if you want to charge a SEALED lead-acid battery. If the charging voltage is only slightly overrated, then production of H2 and O2 is invoked, which can show really dramatical consequences!!!

What charging voltage is recommended?
At 20°C ambient temperature maximum charging voltage should be 2.3V per cell. So, if three cells are involved charging voltage should NOT be greater than 6.9V.
At 40°C ambient temperature, which is the temperature which must be taken into consideration by those forum members who are living in tropical environments, maximum charging voltage should not be greater than 2.2V per cell. So, you will need a constant voltage source providing a charging voltage of exactly 6.6V.
Unfortunately your charging voltage is 8.0V, which is much much too high. With your circuit the continuous production of H2 and O2 gas must be expected, which can be very very dangerous!!!
Ok, there are still two diodes in your circuit, which help to decrease the voltage a bit, but they will not provide this certain amount of voltage which is needed to guarantee that voltage at battery will not rise above 6.6V!
Even by decreasing SMPS voltage to less than 8.0V this will not solve the problem. This can only do a true constant voltage source.

Your circuit shows another disadvantage:
For reliable functionality battery voltage must provide a minimum voltage of about 6.0V. Then, keeping in mind that about 0.5V is dropping across 1N4007 diode, 5.5V is at input of LDO regulator. So, input to output differential voltage of regulator is 0.5V, which aggrees with the specifications.

But: A battery voltage of 6.0V means a voltage of 2.0V per cell. So, only about 30% of total charge of battery can be used with your circuit!

So, why not using a 12V lead-acid battery? Then, you don't have to use this LDO regulator and much more charge of the battery is available.
A suited circuit for experimenting can be found here:

http://www.8052.com/forum/read.phtml?id=71623

Kai