Lithium batteries cost more up front, but in the long run they are superior to lead acid batteries for
several reasons. They are maintenance free, extremely efficient, safe, can be recharged very quickly,
and offer an expandable battery solution. Lithium batteries are cheaper long-term and are more
tolerant to infrequent full recharging and excessive discharging than their lead acid counterparts. They
make the best battery solution for high demand applications, where lead acid batteries do not and will
not survive.
Cost
On the surface, lithium batteries can appear too expensive, but we believe they are one of the best
investments one can make for their system. While the upfront costs for lithium may be higher than
other battery types, the associated benefits like longer service life, superior reliability and excellent
efficiency, will far outweigh the high initial cost. In just about all cases lithium batteries have a lower
cost per KWH per cycle. This means throughout their life cycle they will cost much less than other
batteries and thus will be the most economical solution in the long run, especially when compared to
that of high-quality lead acid batteries.
Maintenance
Many customers contemplating the switch to lithium will be replacing an existing lead acid battery bank
of some type. A flooded lead acid battery bank will require a significant amount of maintenance
throughout its life to stay healthy. Poor maintenance is a leading cause of premature failure for flooded
lead acid batteries. The electrolyte level should be checked regularly to prevent the battery from
running dry, and the battery must be filled with distilled water when electrolyte levels are low. Checking
the specific gravity from time to time is needed to guarantee the batteries are fully charging.
Additionally, the battery must be equalized when the electrolyte starts to stratify to maintain efficiency.
These common maintenance procedures can become mundane and are often forgotten, which can
cause a flooded lead acid battery to fail early. A lithium battery is completely maintenance free,
eliminating the need to add water, check specific gravity, or equalize charge.
Tolerance
Another significant contributor to premature failure of lead acid batteries is excessive discharge and
deficit cycling. Regardless of whether you have a flooded, AGM, or Gel type battery, a 50% depth of
discharge (DOD) limit should be observed in order to prolong their life cycle. Deficit cycling is also very
harsh on lead acid batteries. This happens when a battery is discharged before having the chance to fully
recharge. Plate swelling, loss of active material, and sulfation of the plates can be caused by excessive
discharge and/or lack of full recharge. To achieve the longest life possible, it’s very important not to
over discharge lead acid batteries and to make sure they get completely recharged every cycle.
Unfortunately, this can be difficult to manage, and you may find yourself constantly worrying about your
battery health. Lithium batteries are a worry-free alternative. It’s not necessary to fully recharge lithium
batteries every cycle and most have internal protections within the battery that will never allow you to
discharge down to the point of permanent damage. Generally, you can discharge most lithium batteries
to about 20% remaining capacity every day without shortening cycle life. Lithium batteries can also be
fully discharged periodically without significant adverse effects. You can use them, abuse them, and they
will suck up the energy you give them and spit it right back.
Efficiency
In several applications (especially off-grid solar), energy efficiency is of crucial importance. The typical
round-trip energy efficiency (discharge from 100% to 0%, then back to 100% charge) of a brand-new
lead acid battery is around 80%. The round-trip energy efficiency of a lithium battery is 92-98%
throughout the entire life of the battery. The charging process of lead acid batteries becomes
particularly inefficient once the absorption state of charge has been reached. This can result in
efficiencies of 50% or even less in systems with oversized battery banks or failing batteries. As a lead
acid battery ages, internal resistance builds up and the battery bank becomes even less efficient, causing
more and more energy to be converted into heat rather than stored within the battery bank. As lithium
batteries age, usable capacity is reduced but the efficiency is still maintained.
Charge Time
In most cases lithium batteries can take on more power than can be delivered to them. Charge and
discharge current limits for lithium batteries are often portrayed as capacity scalars. For example, most
lithium batteries can be discharged and recharged at a continuous rate of .5C or half the overall
capacity. Some manufacturers rate their batteries with a discharge and recharge limit of 1C. In this case,
a lithium battery can be completely charged in just one to two hours from 0%. It’s also important to
note that a lithium battery is usually between 95%-99% full charge after the completion of the bulk
charge stage. In contrast, most lead acid batteries shouldn’t be charged at a rate greater than .2C, and
the battery will achieve a maximum of only 75%-80% full charge once the bulk charge stage is finished.
After this, an additional 3-4 hours of absorption charge is necessary to fully recharge most lead acid
batteries.
Safety (BMS)
The safety and reliability of lithium batteries is a big concern, so nearly all lithium battery solutions will
use an integrated Battery Management System (BMS). The BMS is a system that monitors, evaluates,
balances, and protects cells from operating outside the "Safe Operating Area." The BMS is an essential
safety component of a lithium battery system, monitoring and protecting the cells within the battery
against over current, under/over voltage, under/over temperature, and more. Another essential
responsibility of the BMS is to balance the pack during charging, guaranteeing all cells receive a full
charge without overcharging.
Expandability
One of the most significant advantages of lithium batteries over that of a lead acid alternative is that
lithium battery banks can be expanded throughout the life of the battery. This is not an acceptable
practice for lead acid batteries as the result usually ends in significant premature failure of the whole
battery bank. Being that lithium batteries don’t suffer from lack of full recharge or deficit cycling
amongst other things; the addition of new batteries simply increases the storage capacity and reduces
the load on the rest of the batteries. In most cases, this will increase the life of the battery bank. Thus,
making for a whole lot more flexibility in the design on an off-grid system and can allow one to build up a
system as needed and as a budget allows.
