Lead Acid Batteries – AGM Batteries – Lithium Batteries
If you are reading this, it means that you are considering which battery type best fits your particular needs. Lead Acid batteries despite being around for over 100 years are still being sold and used in many applications. AGM Batteries are a step up from lead acid and bring to the table great benefits which we’ll discuss at length. Lithium Batteries are the newest technology, but it has taken awhile for them to pick up steam and we’ll discuss the reasons why and why they are now building a lot of momentum.
In Lead Acid Batteries as the name would imply, the electrodes and grids are made of lead. There is normally some other additive mixed in with the lead, such as calcium to give some mechanical strength. Polarity of the plate is determined by the active material that is placed in physical contact with the grid. The active material is some formulation of lead oxides. The electrolyte is sulfuric acid which in some cases can cause burns when in contact with skin and may produce gases during normal charge and discharge cycles which can be toxic and explosive. Lead acid is still being bought as it continues to be cheap to purchase for starting applications on vehicles but in other applications such as marine, RV and other renewable energy applications Lead Acid is no longer the battery of choice one of the safety factor, the maintenance factor and three Lead Acid Batteries are no longer considered the cheaper alternative because they offer a higher cost per charge cycle than AGM Batteries and even Lithium Batteries (Which have come down in price considerably in the last 3 years).
Depending on the depth of discharge (20- 25% is the recommended discharge rate) Lead Acid Batteries can typically last only between 200-300 charge cycles. The reason for its short life is grid corrosion of the positive electrode, depletion of the active material and expansion of the positive plates. Typically choosing Lead acid means higher weight to stay within the 20 to 25% discharge rate. Lead Acid Batteries have a high self-discharge rate of 40% per year and a poor charge efficiency of 15 to 25% meaning if you have a 100 AH bank you must produce from your solar panels or generator about 115 to 125 AH to fully charge the battery which in the case of a renewable energy system could mean more solar panels needed or longer generator running time.
AGM Batteries (Absorbed Glass Mat), there is a thin ultra-fine fiberglass mat sandwiched between the plates that are saturated with battery acid to about 95% of what they can hold. This mat is then packed in between the plates and slightly compressed, then welded in place. Because the mats are packed so tightly, they are almost immune to vibration. AGM Batteries have been the choice of the military since 1985.
AGM Batteries charge about 5 times faster than Lead Acid, can have a charge efficiency of 2% (sometimes referred to as the internal battery resistance) Example. If you have to charge a 100 AH battery, you will need to produce only 102 AH to fully charge the battery. AGM Batteries outlast lead acid batteries in life cycles since they typically last more than 1200 charge cycles (at 25% discharge rate).
AGM Batteries have a low self-discharge rate of 3% and when compared to traditional lead acid batteries offer a much lower price per charge cycle. (Click on image bellow for pricing on different size AGM Batteries)
On marine applications AGM Batteries are at this moment without a doubt the most popular choice for day sailors and cruisers alike because of the before mentioned safety factors and their ability to not be affected by the motion of the vessel but there could be change on the horizon.
Lithium Batteries are the new boy on the block but up until now most people would immediately rite them off because of their higher price tag. In the last few months the price of Lithium Batteries has dropped considerably making them a real contender on all battery applications. (Click on image below to see latest prices on different size Lithium Batteries).
Advantages of Lithium Batteries VS Lead Acid Batteries
1. Lithium Batteries are 70% lighter than the same size lead acid battery.
2. Orientation: can be mounted and operated in any direction.
3. Rapid charge: a Lithium Battery can be fully charged in one hour from a completely dead battery.
4. No Voltage drop: Voltage Curve is nearly flat giving out higher voltage and power throughout the entire charge cycle. A 12 V Lithium battery has little to no voltage drop while cranking your engine, this provides a 25% faster starting than with lead acid. (when cranking your engine with a lead acid battery the voltage can drop to 9V causing your starter to spin slower).
5. Charge Efficiency: When charging a lead acid battery, you can lose between 15 to 30 % of the energy from your charger due to heat loss and internal battery resistance. A Lithium Battery is 99.1% efficient and will accept nearly 100% of the power coming from your charger or solar panels.
6. Charge Algorithm: Lead Acid batteries heat up and swell if they receive constant current, so charger manufacturers create algorithms to slow down the current flowing into the battery to protect the battery from overheating. Companies like Smart Battery have built their lithium batteries so that they can be charged with constant current and constant voltage. This means that almost any battery charger regardless of the algorithm can charge the battery.
7. No Self Discharge: Lithium Batteries can hold a full charge over 1 year and has virtually no self-discharge.
8. Amp Hours: A lead acid battery’s rating is usually specified at the 20-hour discharge rate. At high rates of discharge above 20 A the usable capacity can be reduced to less than half due to something called “Peukert’s Effect”. (A 225 AH Lead Acid Battery at an 80 A discharge rate may only run for 53 minutes)
Whereas a 225 AH Lithium battery at an 80 A discharge rate can last up to 3 hours.
9. Higher Energy Density: 4 times higher than Lead Acid Batteries.
10. Superior “Usable” Capacity: A Lithium Battery can be fully discharged down to 100% without damaging the battery meaning that if your application requires 200 AH a 225 AH Lithium Battery will be sufficient whereas you would need 3 to 4 times that amount in the case of Lead Acid Batteries.
11. Higher amount of Charge cycles: A typical Lithium Battery life expectancy is between 2000 to 4000 charge cycles as compared to a typical Lead Acid Battery life expectancy of between 200 and 300 charge cycles you are getting more than 10 times the amount of charge cycles with a Lithium Ion Battery.
All these added benefits make Lithium batteries the perfect choice in most renewable energy applications, marine applications, RVs, etc. The recent lower prices and the improvements in safety as well as the easy plug and play connection and compatibility with almost any charger or charge controller is making everyone stop and take a second look at Lithium Batteries.