The following charging methods are recommended to insure a long battery life (Always use a voltage regulated charger, with voltage limits set as described below):

BlueTop Type: BT SLI 4,2
These batteries are designed for engine starting applications. They are NOT recommended or warranted for use in deep cycle applications.

Recommended charging information:

Alternator:
13.3 to 15.0 volts, no amperage limit.

Battery charger:
13.8 to 15.0 volts, 10 amps maximum, 6-12 hours approximate.

Rapid Recharge:
Maximum voltage 15.6 volts (regulated).
Maximum current: No limit as long as temperature <50°C (125°F).
Maximum recharge time: Charge until current drops below 1 amp.

Float charge:
13.2 to 13.8 volts, 1 amp maximum current, time indefinite (at lower voltage).

All limits must be strictly adhered to.

Blue Top Type: BT DC 4,2 / BT DC 5,5
These batteries are dual purpose. They are designed for engine starting and deep cycling applications and for use in boats with large accessory loads.

Recommended charging information:

Alternator:
13.65 to 15.0 volts, no amperage limit.

Battery charger:
13.8 to 15.0 volts, 10 amps maximum, 6-12 hours approximate.

Cyclic Applications:
14.7 volts, no current limit as long as battery temperature remains below 50°C (125°F). When current falls below 1 amp, finish with 2 amp constant current for 1 hour for BT DC 4.2 and 3 amp constant current for 1 hour for BT DC 5.5.

Rapid Recharge:
Maximum voltage 15.6 volts (regulated).
Maximum current: No limit as long as temperature <50°C (125°F).
Maximum recharge time: Charge until current drops below 1 amp.

Float charge:
13.2 to 13.8 volts, 1 amp maximum current, time indefinite (at lower voltage).

All limits must be strictly adhered to.

Safety Information:

Always wear safety glasses when working with batteries.

Always use a voltage regulated battery charger with limits set to the above ratings. Overcharging can cause the safety valves to open and battery gasses to escape, resulting in premature failure. These gasses are flammable! You cannot replace water in sealed batteries that have been overcharged. Any battery that becomes very hot or makes a hissing sound while recharging should be disconnected immediately.

Failure to fully charge a battery can result in poor performance and a reduction in capacity