Product Details
Battery Tender PLUS is lightweight, compact size makes it ideal for those hard-to-fit spots. The trickled charger with a brain will assure batteries are maintained after charging and allows ready to go!

• Fully automatic two-stage lead-acid battery charger. Perfect for all lead-acid, sealed maintenance free and gel cell batteries.

• SuperSmart™ Charging Technology.

• After reaching peak 14.4 VDC, charger automatically switches to 13.2 VDC float voltage.

• When voltage drops below 12.6 VDC, charger resumes charging back to 14.4 VDC.

• Solid state two color LED indicates stage of charger.

• Spark proof.

• Reverse polarity protected.

• 12' output cord.

• 5 year warranty.

• 3-Step Charging (Initialization, Bulk, Float)

• Short Circuit Protected.

You will never have a dead or weak battery because  your car was sitting too long!

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It's so EASY!  The connector cord and female connector head simply connect to your battery and stay connected.  Plug it in to the charger connector and keep it plugged in for a constant trickle charge.  It will only come on when your battery starts to get low. When not in use it simply tuck the connector cord (yellow Arrow) up inside the engine compartment.  Start your car and drive away.  You never have to open the hood.  

1. How can I tell if my battery is charged or not?

Lead acid batteries are made up of cells. Each cell is approximately 2 volts, so a 12-volt battery has 6 individual cells. It turns out that a fully charged 2-volt cell has a voltage of approximately 2.15 volts. Oddly enough, a fully discharged 2-volt cell has a voltage of 1.9 volts. That’s only a difference of 0.25 volts on each cell from fully charged to fully discharged. So a 12-volt battery will measure at about 12.9 volts when it’s fully charged and about 11.4 volts when it is fully discharged. That’s a total of 1.5 volts that represents the full range of charge on a 12-volt battery. To make a good guess at how much charge your battery has left, you can assign a percentage of charge remaining that is directly proportional to the battery voltage. Let’s see how we can do that. If the battery voltage is 12.15 volts, how much charge is left? Beginning with 11.4 volts representing no charge or 0% charge available, subtract 11.4 volts from the voltage that you read. So 12.15 – 11.4 = 0.75 volts. Since there are only 1.5 volts above 11.4 volts that represents the full range of charge, we can divide the difference that we just calculated by 1.5 volts to get the percentage of charge remaining. 0.75 volts / 1.5 volts = 0.5 or when expressed as a percentage, multiply by 100 and get 50%. Here’s the procedure written as a formula that is applicable to 12 Volt Batteries:

OPEN CIRCUIT BATTERY STATE OF CHARGE CALCULATION

% Charge = SOC

% Charge = ((Measured Battery Voltage – 11.4 volts) / 1.5 volts) x 100

Equation 1
That seems easy enough. So what’s the catch? In order for this formula to work, the battery must be in a rest state. In other words, the battery should not be supplying power to any type of load. The experts say that the battery should remain at rest for at least 24 hours to get an accurate measurement, but in a pinch a couple of hours are good enough to make a reasonable guess. Even if the battery is connected to a load, as long as the load current is less than 1% of the battery capacity in amp-hours, then this method is probably good enough in most cases. It’s all a matter of how accurate you want to be. If you’re a scientist or engineer trying to develop a battery powered product, then you probably want a more accurate measurement than if you’re going fishing for the weekend and you just want to know if you need to take the time to charge your battery before you use it. There is one more thing to keep in mind. The only way to be absolutely sure that your battery is fully charged is to do a load test. It is best to have the battery dealer do this for you. We only mention it here because it is possible for a battery to indicate a good voltage, but then immediately when you try to use it, it acts like it’s dead. This doesn’t happen very often, but it’s good to know that it is a possibility.

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2. How long will it take to charge a battery?

We can make a pretty good guess by just dividing two numbers:
Approximate Recharge Time Calculations

(Battery Capacity) / (Charger Current) = Hours
(Amp-Hours) / (Amps) = Hours

Equation 2
Suppose I have a 50 Amp-Hour battery. That’s a fairly typical size for an automotive engine start type battery. Now let’s say I have a 10 Amp charger. (50 Amp-Hours) divided by (10 Amps) = 5 Hours. So we would estimate that it will take a good 10 Amp charger about 5 Hours to recharge a 50 Amp-Hour battery. Actually this rough estimate usually tells us how long it takes to recharge the battery to about 80% of its capacity. To complete the recharge of a battery to 100% with a 3-step charger, it turns out that it will probably take an equal amount of time, or another 5 hours to recharge the last 20% of the battery capacity. To complete the recharge of a battery to 100% with a 4 step charger, in most cases it will take less time than with a 3 Step Charger to recharge the last 20% of the battery capacity. These times are different for all of the software versions.

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