jaylisto:
since i have 12v motorcycle battery charger then i think its more efficient buying 12v battery , so that i will no longer buy sla 6v battery charger.
Make sure that charger can work with an SLA. Also note that an SLA is not the same as a Sealed Battery - generally, SLAs are also known as "gel cell" batteries, because the electrolyte in them is a gel, not a liquid. There exist lead-acid batteries that are sealed (ie - no removable vent plugs to add water or acid to the battery), but they -aren't- "sealed lead acid" (SLA). They have liquid electrolyte in them - not gel. Confused yet?
Now - battery chargers designed to charge liquid electrolyte lead-acid batteries -should not- be used to charge SLA gel cell batteries, unless the charger is designed to be used on such batteries. If you try to use such a charger on an SLA, you'll damage the battery at best; or cause a rupture of the battery (or an explosion!) at worst.
jaylisto:
if i can charge sla 6v battery by my 12v motorcycle battery charger, then i will go for 6v..
It's unlikely you'll be able to do this, unless it has a setting (or sensing capability) explicitly for a 6 volt SLA gel-cell battery. If it is 12 volt only - you /DO NOT/ want to try to charge a 6 volt SLA gel-cell with it (unless you hook two 6V gel-cell batteries in series, and the charger is designed for gel-cells, of course). Doing so is to invite explosion and fire into your life.
jaylisto:
o by the way, im here in the philippines, i will try to find sla 6v battery charger and 6v sla battery tomorrow so that i can plug it directly not regulating the volts anymore... thank you so much.
Whatever you do, match your charger with your battery; try to look up the datasheet for the battery and find out it's 10C rate of charge. Some batteries can be charged quicker than 10C - but you need to review the datasheet of the battery for this. Also note that not all chargers are built the same; some cheap chargers are nothing more than a simple wall wart - if you don't carefully time the charging of the battery properly, you'll ruin the battery easily. Do some research on how to charge gel-cells. There are ways of doing it with a proper current and voltage limiting bench power supply, but even then you have to monitor the charging, voltage and current levels.
Also - any lead-acid battery (sealed, non-sealed, gel-cell, whatever) has to be "maintained" in order for it to perform properly. You can't store them without putting a charge into them, and you must "top them up" periodically (every month or so) and not let them discharge. Generally, if a 12 volt lead-acid battery falls below 10 volts or so (1 volt per cell), it is "dead", and you should consider buying another. What happens is called "sulfation" of the plates; with a proper charger, this sulfation can -sometimes- be removed, but in many cases there's no hope for the battery; properly recycle it, and buy another.
I'm actually planning on buying the following charger after reading some real good reviews about it:
It ain't cheap - but neither are the larger gel-cells in the long run...