Charging Lithium Iron Phosphate Batteries Safely and Efficiently
For the purpose of this article any time I reference lithium, I’m referencing LiFeP04 – Lithium Iron Phosphate.
I’d also like to take a minute to confirm the safety of LiFePO4, this chemistry is NON FLAMMABLE! It is other lithium chemistries that can burn!
How do I store my LiFePO4 battery when not using the RV?
The first thing to note is that lithium batteries do not get damaged when left partially charged, like lead batteries do. When we reference long term storage, 3 months plus is a good benchmark to use.
Most lithium batteries will discharge around 2% a month, so with no loads running, when in storage, it is recommended to charge the battery to 100% at least 6 monthly.
For most of us in RV’s, if you have a battery isolator and or main fuse off the battery, turning the isolator off or removing the fuse is all you need to do.
You can then safely leave it for 6 months. When it will likely be around 88% SoC, reconnect, give it a full charge to 100%, turn off the isolator and leave for another 6 months.
The other scenario, is where it is not possible/practical to fully isolate the battery. In my rig as an example, I run monitoring gear, even when in storage, that draws around 12W or 1 amp, so isolating does not work for me. What do we do for this circumstance? For me, my battery will be at 50% after about 3 weeks. I’ll need to give mine a top up charge at least every three weeks. Those are the sort of calculations you should be making and charge accordingly.
At what SoC do I store my LiFePO4 Battery?
Unfortunately, you can read 10 articles and get 10 answers to this question. Usually anywhere between 50 and 100% and in my experience so long as you are storing lithium in that range you should be fine.
Over Charging a LiFePO4 Battery
Over charging lithium can cause irreversible damage to the battery. This is one area where quality shows through, many people miss the importance of checking this when buying and it will be one of the differences between a $800 battery and a $1500 battery as an example.
I am aware of 100Ah lithium batteries that have recommended charge rates as low as 20 amps, against most quality batteries which are 50 to 100 amps. The big issue here is if you are running moderate to high loads the low charge rate does not give you enough scope/time each day to recover the battery from the loads used.
Most BMS (Battery Management System) protection is by way of maximum charge voltage, not maximum amps so the BMS does not give you protection from higher than recommended amperage charging!
The effect of overcharging is not dangerous, however what happens is eventually the battery cells will swell and die. This usually does not happen on day 1, week 1, month one or even year one, it’s like death by 1000 cuts!
Many early mains chargers and also a lot of multistage chargers never stop charging, once the battery is charged they remain on trickle full time. No batteries like this (including AGM’s), so if you park up long term and want to plug into mains to run a charger, either buy a charger with “storage mode” or buy an electronic timer that can rest the battery.
If you park your vehicle outside and it has solar, the solar should be more than adequate to maintain the battery and it is then resting at night.
What Does It Mean?
Unfortunately, this does get a bit complicated and is the cause of much confusion and many a happy hour debate.
Some (usually better quality) lithium’s are designed to be charged by standard AGM or Gel chargers, without impacting the manufacturer’s warranty for the battery, they are designed this way to be plug and play with existing systems.
Right away, we’re faced with a situation. In this, you can safely charge lithium with non-lithium compatible equipment. Regrettably, this isn’t a fixed rule – it changes from charger to charger and battery to battery.
As a result, it’s not advised to simply purchase a lithium-compatible charger.
This advice applies whether the charger is for solar or mains. This recommendation is due to several reasons which we’ll discuss next.
- All lithium batteries have either a max charge voltage or a voltage charge range.
- When you buy a charger, knowing it is lithium compatible is unfortunately not enough.
Here’s why, reputable brand X battery has a max charge voltage of 14.2V (this is low by lithium standards) and brand ABC reputable charger with lithium mode charges to 14.4 or 14.6 (two very common lithium max charge voltages).
If you are not aware of the actual spec of your battery and charger, and you have tried to do everything right, your battery is going to die prematurely due to overcharging.
In the case of Brand X above you would need a charger of the same brand as the battery, or a charger with a Gel profile (usually 14.2).
This is an issue with these very common brands of non-lithium power products:
- J35C very common in Jayco’s
- Schaudt EBL found in many Euro RV’s
- Some Redarc
- Some Projecta
- Sargent units
- Some CTEC and the list goes on.
With all these non-lithium units, they are fine running lithium’s so long as you know and have confirmed that the spec of your batteries matches the unit and they are a lithium designed to run on AGM or Gel profile, but equally there are lithium’s that shouldn’t be run off these units due to the battery spec not matching.
This is probably the biggest risk area you face as a buyer, from my comments above you can see that lithium compatible chargers don’t suit all lithium batteries and some non-compatible chargers suit some lithium batteries.
Navigating the intricacies of LiFePO4 battery maintenance can be complex, but the team at Motorhome Solar is here to help. If you’re a motorhome or caravan owner and need guidance on handling lithium batteries safely, effectively, and with longevity in mind, reach out to us.
From understanding the specifics of your battery system to advising on storage practices and charger compatibility, we’re here to help you. Let’s preserve the life of your lithium-iron phosphate batteries – get in touch.
So please when buying, check the spec of your gear and buy a battery that matches or it could be an expensive mistake, or if your not confident reading spec sheets, talk to someone who is.
It should also be noted that DVSR’s and VSR’s (alternator charging) are not recommended for lithium as puts too much pressure on the alternator DCDC should be used here.
If you have a multistage mains charger that has any form of recondition stage, do not use it with any lithium battery.
There is a lot to it and we haven’t even touched on sustainability!
The best advice I can give is: Check the spec, check the spec, check the spec! It could save you a lot of money!
Kind Regards, Wayne Hunt