The speed in which Sealed Lead Acid (SLA) rechargeable batteries can charge is based on the type of charger you are using, how much of a charge is left in the battery itself and if the battery is still functional and has not exceeded its life.
Typically, the larger the current coming out of the charger, the faster the battery can fully recharge. The average time it takes to charge a sealed lead acid rechargeable battery is anywhere from 12 – 16 hours and up to 48 hours for large stationary batteries. Sealed Lead Acid batteries are not very quickly replenished and do not recharge as fast as other battery systems.
To estimate the amount of time it will take to charge a fully discharged sealed lead acid battery, divide the batteries amp. hours by the rated output current of the charger, then multiply the resulting hours by 1.75 to compensate for the declining output current that occurs during the charge cycle.
There are many different chargers on the market for different situations. Speed is always a good thing when selecting a charger, but also keep in mind that each type of charger has its own unique benefits that need to be weighed. Sometimes speed will be compromised in order to reap other benefits. Talk to a charger supplier prior to purchasing one and see what they feel will be the best fit for your situation.
The simplest and least expensive sealed lead acid battery charger is a float charger. A float charger can be connected to a SLA battery across the output almost indefinitely. A float charger comes with a standard DC power supply and applies an output voltage of around 2.25V per cell in the battery. A 6 volt battery having 3 cells would amount to 6.75V of output power where as a 12 volt battery having 6 cells would amount to 13.5V of output power.
The typical charging time of a sealed lead acid battery float charger is 16 hours. The float charger will allow your SLA battery to operate its standard full operating life. If you can live with a slower charge time, this is the least expensive alternative.
Two Stage Charger
To achieve a faster recharging time, a lot of people use a more expensive two stage charger. The two stage charger combines an initial constant current bulk charge with constant voltage top-up phase. This charger will automatically monitor the charging process switching between the phases and shutting down the charge. This charger will complete charging in 5-6 hours.
Three Stage Charger
There are also three stage sealed lead acid battery chargers. The three stage SLA charger basically adds one more step for the charger to monitor and complete. Instead of the charger shutting down after the second phase, it goes into a low float charge mode and keeps the battery at a fully charged state.