By Greg Illes
Lithium batteries have truly extraordinary advantages for certain types of RV life — but they have their “dark side” as well. You need to be very well informed to make the “lithium decision.”
First off, NO, they won’t catch fire
There are literally dozens of lithium battery chemistries extant, and the one used in vehicles is lithium-iron-phosphate. Those chemical symbols are Li, Fe, and P, so the batteries are called LFP batteries (or occasionally LiFePo). The iron-phosphate chemistry does NOT have the “runaway” thermal characteristics of other technologies, and LFP batteries simply cannot self-incinerate.
Now that the main hurdle is behind us, let’s look at all the pros and cons. There are quite a few.
LFP Batteries are “nearly perfect” in operation
By this, I mean to say that LFPs are incredibly efficient and flexible compared to lead-acid (LA) batteries.
- Charge very quickly — Can easily charge at 100% of rated capacity (LA limited to 10-20%). This means that a full charge can be reached from a full discharge in typically only a few hours, whereas LA batteries can take a full day or more to fully charge.
- Discharge huge currents with no penalty — Can discharge at 300% of rated capacity with no reduction in lifespan or capacity. LA batteries will take at least a 50% hit in capacity and life if routinely discharged at more than 10% capacity.
- Can be discharged to 95% with no penalty — LA batteries will lose 50% of life or more if discharged to more than 50%.
- No problem being left at partially charged levels — LA batteries will lose 50% of life if kept at partial charge states. LFP batteries actually like being partially charged, and it can even increase their life.
- About 1/4 the weight and 1/2 the size of an equivalent LA pack — In addition to smaller/lighter, LFP also can be mounted in any position/orientation; as an added bonus, they require no ventilation.
- Slightly higher output voltage — at 13.3V nominal instead of LA’s 12.6V, lights burn brighter and motors turn faster. Everything works just a little bit better.
Here’s a typical real-life example of how this works out: My microwave oven draws about 120A out of my power inverter. This causes about a 0.8V drop on the supply lines, which brings the inverter voltage down to 11.8 when running on LA. The inverter sees the battery as “discharged” and kicks off to save the battery. But on LFP operation, the voltage goes from 13.3 to 12.5, and the inverter is happy as can be.
Furthermore, the 120A draw, which would impair LA capacity and lifespan, is “no problemo” for the LFPs. And when I’m done microwaving, the LFPs suck up everything that my solar panels or engine alternator want to provide — there’s no “float charge” charging resistance on LFPs like there is on LAs, and they charge back up again at warp speed.
Microwave, hair dryer, vacuum cleaner, electric power tools, you name it — they’re all welcome in my coach.
LFP Batteries are very touchy to manage
LA batteries will take certain types of abuses that are simply fatal to LFPs. LFPs require much more precise management.
- VERY sensitive to over-charging or under-charging — If an LFP is discharged below about 10.6V, or charged above 14.6V, IT WILL DIE. That’s an unrecoverable, expensive proposition. And dead is dead, no CPR, as in throw it away.
- MUST HAVE battery-management system (BMS) to protect from over/under charge — It’s possible to manually manage charging and discharging, but sooner or later a mistake will be made, with expensive results. The ONLY way to manage LFPs is with an automatic electronic BMS. These can be done inexpensively, but they have to be reliable in the extreme; and they are a possible point of failure.
- Significant up-front cost — LFP systems can range from $1000-$5000 or more, depending on capacity, sophistication of the BMS, and installation costs. A much longer lifespan helps to offset the per-year cost, but it’s still a big chunk of change all at once.
- Not fully compatible with existing engine alternators, solar chargers, and shore-power converters — An alternator typically puts out 14.8-15.5V at no-load, and it will trip a BMS. This must be managed, but there are multiple choices how to do so. Chargers and converters have a different issue, in that they will tend to “see” LFPs at 13.6 as fully charged when they still have much capacity remaining. Again, there are multiple choices to manage this — all of which add to the system expense.
- Narrower operating temperature range — LFPs are typically rated at -20 F to +140 F, while LAs will see -40 F to +160 F ratings. Not that big a deal for most of us. BUT there’s a larger concern: LFPs also should not be charged below 32 F, and this can require battery heaters if they are operated near freezing temperatures; installing them in a heated area is also an option.
- More complicated to get service and replacement parts — It’s easy to get another 12V LA battery at any auto parts store. (Maybe not exactly the one you wanted, which can be a problem when running batteries in parallel, but that’s a longer discussion.) But LFPs are going to be special order anywhere you roam, and it could take many days to get a replacement. This requires a “fall back” strategy to keep the coach operational in the case of an LFP system failure.
When I installed my LFP system I built a semi-custom BMS and attached it to the access cover (the little tab at the back in the photo). Now, in the space where 2-3 golf cart batteries used to live (about 110AH usable), I luxuriate in 360AH of King-Kong style capacity.
If this all sounds complicated and difficult, well, yes, it is and can be. Although there are some “drop-in” LFP batteries with built-in BMS modules, these tend to not have the extreme discharge currents of a custom system, nor are they rated to operate in parallel. They are also considerably more expensive and not as space-efficient. But for the lower-current/capacity user, they just might be the ticket.
A full custom conversion is not for the faint-of-heart, and being technically savvy and handy is very much an advantage (although there are some LFP systems being delivered as built-in options in high-end expedition vehicles). I would have to say that by far the biggest LFP advantage goes to the boondocker and remote camper. Folks who stay hooked up most of the time, or don’t mind running the generator a lot (gag), really won’t see a benefit.
But I can tell you unequivocally, I’ve had these batteries in my coach for three years now, and I’ll never go back to LA batteries. For one thing, in my small class-A, I could never fit 360AH (usable) of capacity using LA technology. And between my solar panels and engine alternator, my LFP batteries charge so quickly that I never have to use a generator; in fact, I don’t even carry one any more. For us, the LFP advantages far outweigh the disadvantages, and we have gotten very accustomed to running with this incredibly flexible, wonderfully quiet power source.
Greg Illes is a retired systems engineer who loves thinking up RV upgrades and modifications. When he’s not working on his motorhome, he’s traveling in it. You can follow his excellent blog at www.divver-city.com/blog