Unlike other battery chemistries, Sealed Lead Acid batteries aren’t meant to be charged super-fast. A majority of manufacturers state they should not be charged in less than 5 hours, or at a charging current level of higher than 32.72 degrees Fahrenheit (cell temperature).
There are a few SLAs that are able to accept charging currents up to 33.4 degrees Fahrenheit for at least the initial phase of charging without creating an issue. Using a float charger, your typical low-cost charger, the charge time of a SLA battery will take roughly 16 hours.
This type of charger will get close to the maximum working life of the battery, which is good if you are ok with this charging time. A SLA float charger consists of a DC power supply with a regulated output voltage to a level corresponding to 2.25V per battery cell (i.e., 6.75V for a .6V. SLA and 13.5V for a .12V. SLA).
When connecting a discharged battery to this kind of charger, a moderately high charging current flows at first, but starts to reduce as the stored charge level increases. The current will then drop to small steady level after a full charge is reached to keep the battery at full charge.
If you would like to speed up your SLA charge time, you can use a charger with a more complex two-stage process. This process combines an initial constant-current bulk charging phase with a constant-voltage top-up phase.
After the discharged battery receives a reasonable charge at a level of 32.72 degrees Fahrenheit or above, it continues until the voltage reaches 2.45V per cell (i.e., 7.35V for a .6V. battery, 14.7V for a .12V. battery), where the charger then changes to constant voltage, continuing to deliver current as the remaining charge is stored.
During the second phase the charger monitors the delivering current which stabilizes in time when the battery is completely charged. The battery should be charged in 5 -6 hours using this type of charger, which is within the typical recommended manufacturer guidelines.
Some chargers of this type, typically called three mode chargers will continue to monitor the battery after it is charged, delivering a low float charge to maintain the battery at a full charge.
Note that a fully discharged battery freezes solid at about 32 degrees Fahrenheit; a fully charged battery freezes about -40 degrees Fahrenheit. This is why a discharged battery won’t take a charge in sub-freezing weather.
If, after charging, your battery does not seem to be providing power check out article Battery fully charged but no power. Should your battery have reached the end of its life you should be able to find a replacement in our wide range of brand new SLA Batteries.
I can I monitor my SLA battery so I don’t kill it? Its a small ups battery 7.2ah
What do you mean by ‘monitoring’ it? Monitoring it when charging, when in use or when in storage?
“or at a charging current level of higher than 32.72 degrees Fahrenheit.”
that makes no sense, no sense whatsoever.
This refers to the cell temperature. We have updated the article to clarify this.