SLA full charge V?

It's not that simple. Lead acid batteries take a very long time to charge if you just apply 13.8. Smart chargers go up to 14.7 V (bulk charge). At this voltage gas starts to form. Then they then step back to 13.8, the float voltage.

The SLA types actually can be charged with a simple contant voltage with some form of current limit. The best place to look are in the manufacturers datasheets.

Meindert

Read this link about charging lead-acid batteries:

After you have charged a lead acid battery fully and it has sat long enough, untended, for the voltage to settle down, it should read about 12.7 volts for a flooded six cell battery... a shade higher for an AGM. You can judge a battery's charge from its voltage only if it has been sitting long enough for the voltage to settle down.

The only time you are likely to see a battery holding a steady 13.8 volts is when you have it on a float charger with a regulated 13.8 volt output. And the battery doesn't necessarily have a full charge on it even then. Generally, charging a lead acid battery entails gradually bringing the voltage up to about

14.5 volts by putting a constant current into the battery, and then holding the voltage steady while the battery continues to absorb current, and this absorption takes a long time, several hours at least, if the battery was discharged to any appreciable extent before you put it on to charge. You can't take a battery that is somewhat flat, bring the voltage up to 13.8 volts and tell yourself that it is charged. For it to charge, a battery would have to stay on that voltage for a very long time, much longer than charging normally should take. 13.8 volts is not a "full charge." It is a maintenance voltage. As for whether you can use a "wall wart" to charge a battery, often you can, but much depends on whether the power supply is regulated. If it is not regulated, the voltage will vary at any moment (this is a function of current), and this will determine how you use it.