You may not need a special charger if you have a charge of any type of SLA battery; Gel or AGM.  AGM battery chargers are mostly compatible with LiFePO4 batteries but may need a few modifications. If you using a charger for any other type of lead-acid battery it may not charge your battery. A charger with a higher voltage will not charge as the BMS is set to protect the battery from a high voltage. On the other hand, a charger with a low voltage may not fully charge the battery.