pulse charging lead acid battries effects and side effects
Pulse charging a lead acid battery should follow the same technique as for regular charging. Basically, ignore the fact that it is pulsing. Each pulse must have its voltage and/or current limited in the same way for a continuous charge.
Guides on how to charge a lead acid battery are below:

SLA charging basics
Charging Lead Acid

So the simplest way of charging a lead acid battery is to limit the charging voltage to approximately 13.8v for a 12v battery, although this may vary depending on the manufacturer, temperature etc. Also limit the current. A charging current limit of C/10 is typical safe value for car batteries.  (e.g. a 100Ah battery can usually be safely charged at 10A up to 13.8v).
However, I'm not sure why you want to use an H bridge. In fact, depending on how the H-bridge is configured, your pulses will alternate between charging and shorting the battery (half bridge), or even reversing it's polarity (H-bridge) which is definitely not what you want to do.
Why on earth are you using a half/H bridge to do this? Or pulsing at all for that matter? Can you give a circuit diagram of what you were planning? (Use the circuit diagram tool in the text editing box by clicking the tiny circuit button)