The more constant voltage of rechargeable will mess with that gauge, leading people to think their device is defective. (thewirecutter.com)
If the battery is at or below the empty voltage (which for lead acid antimony batteries is at 11.89 V, but the battery can in theory be at any voltage between 0V and 11.89 V and it is in any case approximately empty), and has 48 Ah capacity, a 1.25 A charger will fully charge the battery in approximately 38.4 hours (just divide the Ah of the battery by the amperes of the charger), but I would add few hours more because the end of the charging occurs at constant voltage, not at constant current. (mechanics.stackexchange.com)