Only 12-volt, lead acid, batteries can be recharged by an electrical battery charging device. There are two basic physical types of the lead acid battery, an SLA (sealed lead acid), and an open top maintainable battery. The SLA is just as the name applies; it allows no access to check the level of battery fluid inside each individual battery cell. The open top or maintainable battery allows the user to check and add fluid to the battery. Both of these types of batteries can be easily tested for a full charge.
Attach the 12-volt car headlamp to the positive(+) and negative(-) terminals of the battery. Keep the lamp connected for approximately three minutes. This will remove any surface charge to the battery if it was freshly charged. A surface charge occurs through the charging process and can give a false result to the following test.