Batteries slowly moving to a new era

The previous post referred to a battery upgrade that included a switch from a lead acid to a lithium battery. It appears (good data on this is sketchy) that this produced four times the capacity for size and weight versus a ten times increase in capital outlay. Lithionics is one company that is pushing lithium batteries and its website has some useful information.

Battery life is always one issue. Their FAQ page on this provides a graph of cycles versus depth of discharge but does not mention any other age factors. With 90% DoD, 2400 cycles can be expected while at 10% DoD you might get 35,000 cycles. These are at a 1C discharge rate which is a one hour rate. The usual rating for a lead acid battery is a 20 hour rate and they may provide a range of 500 to 2000 cycles for a similar DoD range.

Lead acid batteries are popular because they are cheap and will take a lot of abuse. Not so lithium. This is why Lithonics pushes its NeverDie® Battery Management System (BMS) to protect the battery from common abuse scenarios. One of the issues it handles is cell equalizing. For RV’s with lead acid batteries that is usually handled by overcharging. Storage will do this with a good battery maintainer but some go for the old style bulk charge while monitoring specific gravity style described on Trojan Battery’s website. The BMS is using modern technology for balance charging cells using cell by cell voltage monitoring as lithium batteries don’t use a liquid electrolyte. This type of charging is also popular for those into remote control hobbies like drones and scale model vehicles that run on lithium batteries.

As for cost, BattleBorn lists an LiFePO4 100 ah 12v LiFePO4 Deep Cycle Battery for $899.00 – Powerstream has a 12v 22AH for $295 so 100 AH of these would cost nearly $1500 – for comparison, Walmart sells a group 29 lead acid RV battery with about this 100 AH 12v capacity at around $100. This is the 1000 watt hour battery capacity level. 

The Journal of the Electrochemical Society has a paper on Calendar Aging of Lithium-Ion Batteries. The abstract concludes “To maximize battery life, high storage SoCs corresponding to low anode potential should be avoided.” Here are some other highlights:

Calendar aging comprises all aging processes that lead to a degradation of a battery cell independent of charge-discharge cycling. It is an important factor in many applications of lithium-ion batteries where the operation periods are substantially shorter than the idle intervals, such as in electric vehicles. Furthermore, the degradation owing to calendar aging can also be predominant in cycle aging studies, especially when cycle depths and current rates are low.

This is particularly important in RV’s and is why cycle life isn’t even much of an issue with lead acid batteries.

Basically, both the evolution of passivation layers and transition-metal dissolution are promoted by a high state of charge (SoC) and temperature

This is similar to what happens in lead acid batteries where the passivation layers is called sulfation. The difference is that lead acid batteries do better with a full state of charge (SoC) while lithium batteries suffer if stored this way.

Battery University has a page on how to Prolong Lithium Based Batteries

Lithium-ion has not yet fully matured and is still improving. Notable advancements have been made in longevity and safety while the capacity is increasing incrementally. Today, Li-ion meets the expectations of most consumer devices but applications for the EV need further development before this power source will become the accepted norm.

That means you need to be careful when evaluating lithium battery specifications and advertising claims. There isn’t a history, things are changing rapidly, and effective measurement standards are not well established.

Environmental conditions, not cycling alone, govern the longevity of lithium-ion batteries. The worst situation is keeping a fully charged battery at elevated temperatures. Battery packs do not die suddenly, but the runtime gradually shortens as the capacity fades.

Batteries are electrochemical devices and suffer much the same issues no matter the chemistry. Lithium batteries have advantages in terms of cycle life, high discharge rates, and short charge times. This might get you a 4x capability improvement for a 10x price premium. Here’s where that might be worth considering.

  • If you want to run your RV air conditioner for a few hours or other heavy loads for more than a few minutes, 
  • If your lifestyle frequently cycles battery charge in a consistent pattern that doesn’t show significant variation or have need for deep reserves.
  • If you have an ability to charge the battery at 1C rates (100 amps for 100 AH battery)
  • If weight is a significant factor for your battery bank.
  • If you don’t have to worry about temperature extremes (below 40F or above 90F)

Otherwise?

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