CAMPING - POWER & LIGHTING
There’s no doubt that lithium ferro phosphate (LFP) batteries are taking over deep-cycle-battery tasks for Australian bush travellers. The combination of fast-charge ability, deep-discharge resilience, constant voltage discharge, light weight and potentially long cycle life is unbeatable, despite the considerable cost penalty.
The RV business globally now has 10+ years of real-world experience with lithium batteries in 4WDs, caravans and campers, so some guidelines have emerged on how best to use and protect your considerable investment in an LFP system.
we’ve known from the outset that LFP batteries need a different charging regime from that for lead-acid batteries, but additional differences have been discovered.
At OTA we’ve been running a Revolution LFP 100Ah LFP battery in our Tray Tek slide-on camper since early 2015. Initially it had a Redarc BCDC on-board charger, but we moved up to a Redarc Manager30 three years ago. This charger seamlessly accepts solar, alternator and mains current inputs.
The LFP system has functioned perfectly since day one, providing ample fridge and light power through daytime solar input, when the sun is shining. In prolonged camping situations without sunlight on our 200W panel we’ve been able to maintain battery level with a regime of only one hour’s mains, alternator or generator input every two days.
When the camper isn’t on the back of our trusty 75 Series tray-back it sits in our back yard for weeks or even months at a time, while the solar panel maintains 100 percent charge, via the Manager30. Like most people with a lead-acid battery background, we thought that was an ideal situation. However, we were wrong, it now appears.
Full charge in storage is not a good thing
What our extensive global research revealed is that LFP batteries do not like being stored at full charge. Something in the 50-70-percent range seems to be ideal. If you did that to a lead-acid battery you’d kill it in no time, but there’s now ample evidence that LFP batteries thrive on storage at partial discharge.
When you buy a new LFP battery to install, you’ll most likely find that its delivery state of charge (SOC) is around 70 percent.
This situation is presenting battery charger manufacturers with some issues, because the ideal on-board charger would seem to be one that will ensure maximum charge levels during times the the battery is doing its camper-power job, but a reduced charge ceiling when the camper is in ‘storage’ mode.
Lead-acid battery chargers have a ‘float’ charge function that constantly trickles in charge, to counter the lead-acid battery’s high self-discharge rate. LFP batteries have very low self-discharge and don’t need a float function. In fact, it seems that constantly maintaining 100-percent charge can be detrimental to the cycle life of an LFP battery.
What’s required may be a simple adjustment to an LFP charger, setting the ‘absorb’ voltage to 14.4-14.6V, so that the battery stops charging at that point. In theory that should result in around 90-percent SOC. A 100Ah LFP battery charged to 90-percent still has a lot more power capacity than a lead-acid one charged to 100-percent, so there would be little real-world loss.
We’ve asked some of the major battery charger companies for their feedback to this proposition, so watch this space for their responses.
Temperature conditions apply
Northern hemisphere research indicates that LFP batteries will not charge once the temperature drops to 0°C. The battery will discharge, but won’t charge. Lead-acid batteries will charge and discharge below freezing.
Another problem is high temperatures, above 30°C, even for LFP batteries being stored. Exposure to high ambients has greatly shortened the life of test LFP batteries.
It seems that the ideal operating environment for LFP batteries is to keep them in the 0°-30°C band. Obviously, under-bonnet installations and mounting battery boxes near hot pipes or against sun-heated, non-insulated camper walls are big no-nos for LFP batteries.