Batteries: How to Keep Your Auxiliary Battery Happy

SLA: All lead-acid (sealed or not) batteries are considered “old school” type batteries, and operate on the same basic principles of battery chemistry. Energy is stored in the form of a chemical reaction, which creates an electric current. This electrical current a battery produces is what powers whatever device is connected to it. The process can be reversed by feeding current into the battery, either with a vehicle charging system, a plug-in charger, or solar panels. This cycle can only be repeated so many times before the materials that make up the battery break down, reducing capacity and eventually leading to failure.

There are a few things to keep in mind to make sure your SLA battery stays happy and healthy: 

• The less a lead-acid battery is discharged between charges, the longer it will last. Charge as often as is practical. The battery in your vehicle is nothing like a cordless drill or phone battery, which are typically nickel-cadmium “ni-cad” batteries. Completely discharging your vehicle battery does no good and is actually harmful, the exact opposite of a ni-cad battery. 

• Whenever the voltage level of a lead-acid battery drops below 10.5 volts, irreversible damage is being done. A good rule of thumb is if light bulbs start getting noticeably dim, stop using that battery until it can be charged up. Most inverters will automatically shut off around 10.5 volts to prevent battery damage. If you have one of our auxiliary battery kits installed, you can use a voltage meter in the 12v outlet to monitor your battery's health.

• A lead-acid battery should always be stored fully charged. The lifespan of the battery will be reduced if stored uncharged; the lower the charge, the greater the damage that will result. A lead-acid battery should never be stored if its voltage is below about 11.5 volts. Batteries also self-discharge, so any battery that is stored should be charged every 6 months or so to prevent it from falling below 11.5 volts. Charging it more often will extend battery life, but do not leave it charging continuously unless the charger is fully automatic (otherwise known as a "smart charger"). Even “trickle chargers” can overcharge a battery if they aren’t automatic. The charger GoWesty sells is fully automatic, and will never over-charge your battery, which is why they cost a little more than your typical garden variety Sears Roebuck trickle charger.

• The faster energy is pulled out of a battery, the less energy will be available. This means that if a 5 amp load lasts for 10 hours, a 10 amp load will not last 5 hours, but in fact less. Taken further, a 50 amp load will not last for 1 hour, but actually much less. Keep this in mind when using high-load accessories. Watts divided by 12 (volts) = Amps. This means a device that is rated at 500 watts draws about 42 amps at 12 volts.

• Inverters are not 100% efficient. The actual number is more like 85%. This means that if a device rated at 500 watts is plugged into an inverter, the inverter will actually draw about 590 watts or about 50 amps at 12 volts. Do not try to charge a battery by plugging a battery charger into an inverter that is connected to the same battery you are trying to charge. It will not work, as the inverter will draw more from the battery than the charger replaces. If this did work, we could all retire as billionaires, and tell the oil companies to get stuffed.

• Battery capacity naturally decreases over time and use. If the capacity has dropped significantly (goes dead much quicker than it used to) it may be close to total failure. If this is the case, have the battery tested and replace it if necessary. Usually, a battery is still considered “good” if it has at least 80% of the capacity it had when new.

LiFePo4: This battery technology is state of the art. Compared to lead-acid technology, it is light years ahead. The weight to power ratio is about double what lead-acid has to offer. They also have a smart circuit built-in to protect themselves from over-discharging or overcharging. You pretty much can’t kill one of these batteries. The two downsides to this battery technology are initial cost and more complicated charging.

Cost: One of these batteries will set you back about double what the same size SLA battery costs. But given their superior performance and better longevity, they end up costing less over time.

Charging: This battery technology requires more sophisticated charging. Simply hooking up your old Sears battery charger, or in parallel (positive-to-positive, negative-to-negative) with your starting battery (and relying on your engine’s alternator to charge it) won’t cut it. To properly charge these puppies requires a smart charger for charging from house current and/or a smart DC-DC charger controller/battery isolator for charging while you drive or with a solar panel. Here again, there is cost and a bit more complexity involved, but well worth it, all things considered.