How do I charge my battery?

All lead-acid batteries contain highly corrosive sulfuric acid, generate explosive gases and have warning labels which should be observed closely. For best results, charge the battery as soon as you know it is discharged. To charge your battery, follow these steps and important safety tips:

What's the best way to charge deep cycle batteries? The maximum charger rate in amps should be 20% of the amp hour rating of the battery.

Normally, deep cycle batteries do not require special charging procedures. However, we recommended that you use a charger designed specifically for deep cycle batteries. It is best to slow charge all batteries, especially deep cycle. The 20% rule should be used when charging a deep cycle battery. That means to choose a charger where the maximum current (in amps) is less than 20% of the Ah rating. For example, an Interstate SRM-27 is rated at approximately 100 Ah, so a 20-amp charger should be the maximum. Also, it is best to use a charger that is adequate to recharge the battery within 10-12 hours (see next question).

How long should I charge my battery and at what current? Generally, we recommend that you use a low amp charge, i.e. as low as the battery will accept, over a longer period of time. A 10-20 amp charger can charge most automotive batteries. Fully charging a completely discharged automotive battery, for example, with a 10-amp charger may take approximately 6-10 hours at a temperature of 80°F. Lower ambient temperatures require a longer charge time.

Some chargers automatically adjust the current and length of charge according to the battery's state of charge and then shut off when the battery is fully charged. If the charger requires manual adjustment for current or shut-off, check the charger's instructions to determine the proper current and length of charge based on your battery's rating.

What will happen if I don't charge my battery properly? The two extremes of improper battery charging are under charging and over charging.

Under charging results from a failure to allow the charger to charge long enough to restore the battery to full state of charge. Continually operating the battery in a partial state of charge or storing the battery in a discharged state will result in a condition known as sulfation. Sulfation reduces the battery's performance and may cause premature battery failure.

Over charging causes accelerated corrosion of the positive plates, excessive water consumption, and in some cases, damaging temperatures within a lead acid battery. Deep cycle batteries should be charged after each discharge and/or after storage of 30 days or more. We recommend that a deep cycle battery not be discharged below a 50% state of charge. Recharging a severely discharged battery (below 50% state of charge) can result in the battery becoming overheated or overcharged.

Where can I find a charger for my battery? Interstate chargers are available through our 320 distributors in the U.S., Canada, Jamaica, Puerto Rico, Dominican Republic and Guam.

What type and size of charger should I buy?
Type: The advantage of an automatic charger is its convenience. Once you connect the charger to the battery, the charger does the rest. Manual chargers are less expensive and equally effective at charging batteries, but they require a greater level of supervision.
Size: In selecting the proper size of charger, you must consider the battery's capacity and the amount of time that will pass between charges. In applications where cycling is infrequent, such as seasonal RV or boat usage, a charge with an output current rating equal to 20% of the battery's rated capacity will suffice. In applications where battery recharge should be accomplished within 12 hours, a three stage, automatic charger may be required.

Why won't my battery take or hold a charge? A battery may not accept a charge for several reasons. Your battery may have a bad cell or an internal short and therefore be irreparable. Or it could be so severely discharged that it will require a professional calliber charger to charge it. Many home chargers have minimum voltages that must be present in the battery before the charger will switch on. Normally these low voltages are well below those exhibited by a battery that appears to be "dead."

Often however, the battery is not given the adequate amount of time to accept a charge. One of the best tips regarding battery charging is to observe the charger's ammeter swing needle (available on some chargers) during the charging procedure. After the charger is connected to the battery and is on, the needle should deflect to a high amperage level if the battery is partially discharged. If the battery is severely discharged, the needle only deflects slightly away from zero. Continue to observe the needle in either situation. On a normally discharged battery only, the needle will start to taper in amperage back toward zero, usually in less than five minutes. This reduction in amperage typically indicates the battery is accepting a charge. On a severely discharged battery, the needle will start off very low then rise. This rise of the needle is a preliminary indication that the battery is accepting a charge.

Always determine the battery's state of charge before and after recharge. The most accurate method (on a removable vent cap battery) is to perform a specific gravity test with a hydrometer. If the battery will not hold a charge adequately, contact the nearest Interstate dealer.

How can I test my charger to see if it is bad? Check the ammeter gauge (where applicable) or the indicator lamp on the charger. If the charger is working properly, the ammeter gauge should deflect to an amperage level above zero once the charger is connected to the battery and is turned on. If the battery does not respond to charging within a few hours, your charger may not be working correctly.

Temperature Effects

    Higher temperatures:

            Increases Capacity, but effect more pronounced at short rates.

            Lessen battery life - 8^oC Increase halves battery life

            Increases gassing and water loss

            Promotes thermal runaway

    Thermal Runaway

            Poor Thermal Management

            *    Heat Generation exceeds heat loss

            *    Impedance is reduced as temperature rises

            *    As impedance is reduced float current increases

            *    Increased float current results in more heat generation

            *    Battery temperature rises

            Cycle broken by system or battery failure

            Preventable by adequate spacing and ventilation

Aging

    Positive Grid Corrosion

        *    Normal failure mode

        *    Gradual loss of capacity with time

        *    Accelerated by temperature

Positive Grid Growth

        *    Caused by corrosion

        *    Can short out cells-may cause runaway

    Dryout

        *    Not a normal failure mode

        *    May be caused by high temperatures-high voltages

Battery Problems

    Ground Faults

        *    Caused by damage to container or uncontrolled venting

        *    Detect by voltage to ground

    Cell Shorts

        *    Caused by contact between plates

        *    Reduces voltage by 2 V on charge-greater during discharge

    Open Circuit Failures

        *    Caused by corrosion of connectors or damage

        *    High charge voltage

        *    Corrosion eliminated by design changes in VRLA Cells

Catalyst for VRLA Batteries

    Benefits

        *    Lower float current

        *    Converts H₂ back to water

        *    Keeps negative plate charged

    Bottom line:    Longer Life