Battery Chargers

The simplest method is to test your battery with a voltmeter to measure the voltage between the positive and negative terminals or posts. While the battery is not being charged and not powering anything, you can use your voltmeter and get a reading. For a 12-volt lead-acid battery, the voltage will be between 11 and 13 volts, depending on the charge. The closer it is to 13 volts, the closer it is to being fully charged. A battery at 11 volts needs recharging. The exact voltage will differ depending on the battery voltage, style, and age.

There's no definitive answer to this question, but you can make a good guess with some simple math.

Our ETX-30L Big Crank battery has a capacity of 26 Ah. You plan on charging this with a 2-amp charger. Using the above equation, you would have [26 Ah / 2 Amp = 13 Hours]. This calculation is a rough estimate and usually tells us how long it will take to recharge the battery to about 80% of its capacity.

To complete the recharge all the way to 100%, it will take an equal amount of time to recharge the last 20% of capacity. Some chargers may get it there a little faster, but there's no absolute guarantee.

The short answer: Overcharging batteries can kill them.

If you leave a manual charger connected continuously, even at low amps, the battery will eventually die. When a battery gets overcharged, the electrolyte inside gets hot, and gases are created. If you have an older vented battery, the electrolyte could evaporate, and your battery plates will be exposed and eventually ruined. Overcharging a sealed battery will cause the gases to build up until the battery balloons out and bursts.

An automatic charger will only charge the battery as necessary, shutting itself off until the battery voltage drops again. Good battery chargers from brands like BatteryMINDer and Battery Tender can keep a battery charged without the risk of damage.

Whether or not you can leave a battery charger on all night depends on the type of charger. If you are using an automatic battery charger, it’s okay to leave it connected overnight since it will know to stop charging once the battery is full. However, manual chargers should not be left on for extended periods, as they can overcharge and possibly damage the battery.

If the battery is deeply discharged but still functional, a charger with a desulfation or recovery mode may help bring it back. However, a fully dead battery may not hold a charge and should be tested or replaced.