What does lithium give you that the old lead acid technology doesn't?
Faster charging and discharging
- Lithium batteries will accept a charge much faster than lead acid. This means your battery can take the charge from your solar panels, DC to DC charger or mains charger as fast as they can give it. This can mean the difference of an hour vs a day to recharge from mains power.
- The fast discharge allows you to run appliances that require a sudden peak load without a serious drop in voltage. This would apply to air conditioning startup, microwave ovens, induction stoves, coffee machines, bread maker, etc.
- A lithium battery can accept 100% of its advertised capacity (100amps per 100Ah) before the battery voltage is affected. This is because lithium batteries have a very low internal resistance. They have a very low internal resistance because they work by lithium ion transfer rather than the chemical reaction that lead acid batteries use. A lead acid battery can only be charged at 20% of its advertised capacity (20 amps per 100Ah capacity) before the battery's internal resistance will cause the battery voltage to rise faster than its true state of charge.
They weigh less per amp hour
- Lithium batteries weigh a lot less than lead acid per useable amp hour. So you can either save some precious weight allowance in your RV, or upgrade to a higher-capacity battery for the same weight.
- For example, a lead acid battery's weight is between 30kg and 32kg per 100Ah. If your 100Ah lead acid battery weighs less than 30kg, it is not a 100Ah battery - you've been ripped off.
- A 100Ah lithium battery weighs 16kg. As mentioned before, a lead acid battery can supply 50% of its capacity from fully charged before it drops below 12V under load. A lithium battery can supply 100 of its capacity from fully charged without dropping below 12V. This means effectively, per useable amp hour, lithium weighs a quarter of the equivalent lead acid.
They like to work
- The days of keeping a close eye on your battery voltage for fear of shortening the life span of a lead acid battery are over when you switch to lithium. Lithium batteries discharge without a serious voltage drop due to their low internal resistance. They don’t have to be returned to 100% state of charge (SOC) each time they’re discharged in order to keep a good cycle life. They like to work, so there is no need to fear shortening their life by working them hard. They will actually thank you for it.
- Lithium batteries don't like to be stored at 100% capacity and don't need to be regularly recharged the way lead acid batteries do. Hard to get your head around, but it's the complete opposite of what you've known about batteries so far.
They have a much longer cycle life
Just how long, we don't really know, as we haven't had any die of old age yet, but let me explain the advertised figures of lead acid and lithium batteries.
- A cycle for a lithium battery is measured by charging the battery to 100% state of charge, then discharging to 0% state of charge. This is one laboratory cycle. However, that's not how most people use their batteries, but we're talking about figures advertised by the manufacturer here.
- A lithium battery will cycle from 100% to 0% state of charge for 1000 cycles while retaining 100% capacity.
- It will cycle a further 4,000 cycles (total 5,000 cycles) and still have 80% capacity remaining
- It will cycle a further 2,000 cycles (total 7,000 cycles) and still have 70% capacity still remaining.
- A cycle for a lead acid battery is measured by charging the battery to 100% state of charge, then discharging to 50% state of charge.
- A lead acid battery will cycle from 100% to 50% state of charge for 600 to 700 cycles before it will permanently drop below 60% capacity, in other words, 10% capacity remaining (they can only be discharged to 50% before they reach end of life).
You can use more of the available amp hours
- A lead acid battery can only give you a maximum of 50% of its available charge before it drops below 12 volts under load.
- Lithium can supply a much higher load without voltage drop or loss of capacity. Let me explain what I mean by loss of capacity:
- A lead acid battery (AGM, gel, flooded cell, lead crystal) has its capacity rated over a 20 hour discharge (C20). This means for a 100Ah battery, the maximum rate you can discharge is 5 amps to still get the full 100 amps - or truly 50 amps to 50%. If you try to discharge the battery faster, some of the capacity is lost. This is known as the Peukert Factor.
- So, if you discharge at a rate of 10 amps, the total capacity of a lead acid battery reduces to 90Ah. Because you can only dishcarge a lead acid battery to 50% before the voltage drops below 12V, you in effect have only 45Ah available if you discharge the lead acid battery at a rate of 10 amps
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Arthur Schopenhauer