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:
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.I know full charge of automotive lead acid batteries is 13.8V. Are gel SLA's, say the 12AH type, the same when used with a "12V" wall plug charger?
If not, can they be charged to 13.8V using an automotive charger?
Thanks,
Robert Myers
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