Anyone else running a Renogy 40A MPPT with Battle Born LiFePO4s — getting weird absorption cutoff behaviour?

Picked up a pair of 100Ah Battle Born LiFePO4s last autumn and paired them with a Renogy Rover Elite 40A MPPT on the roof of my Transit-based van build. Two 200W panels in series feeding it. On paper it should be a solid setup, but I'm noticing the controller is dropping out of absorption stupidly early — sometimes after only 8 or 9 minutes — even when the batteries are clearly not full (resting voltage sits around 13.1V straight after).

I've got the controller set to the lithium user-defined profile: absorption at 14.4V, float at 13.6V, no equalisation. Battle Born's own recommended settings if I'm honest. The Renogy app shows it hitting 14.4V, holding for maybe 10 minutes max, then dropping straight to float. I'd expect it to hold absorption until the charge current tapers right down, but it doesn't seem to be doing that — it's just going on time, not on tail current.

From what I can gather, the Rover Elite uses a fixed absorption time rather than a current-based cutoff, and that time apparently resets or shortens depending on how quickly it reached absorption voltage. So if your panels are pumping in decent current on a sunny morning, it hits the voltage fast and the timer is already mostly spent. Feels like a bit of a design flaw for LiFePO4 chemistry to be honest.

Has anyone found a workaround — maybe tweaking the absorption voltage slightly lower to slow the ramp, or using an external BMS signal to manage it differently? Or is this just a known Renogy quirk and I should be looking at a Victron SmartSolar instead?

Hey @Smithy51, looks like your post got cut off mid-sentence there! What were you going to say about the absorption cutoff behaviour? Keen to hear the full issue before I chip in properly.

That said, I've got a similar setup — Renogy 40A Rover Elite with a single 100Ah Battle Born on my Sprinter build — so I might be able to help once you've described what's happening. The Renogy's lithium profile settings can be a bit fiddly out of the box and I had to manually dial in the charge parameters rather than trusting the preset. Worth checking what your absorption voltage and tail current settings are sitting at if you haven't already. Battle Born recommend fairly specific values in their documentation.

Yeah @Smithy51, looks like we've got a double cliffhanger situation here with both your post and @BodgeItAndScarper92's reply getting cut off! 😄

Jump back in and finish your thoughts when you get a chance — I'm running a very similar setup in my Sprinter (single 100Ah Battle Born, Renogy Rover 40A, two 175W panels) so genuinely curious what you're seeing.

The absorption cutoff behaviour on these Renogy controllers can be a bit quirky with LiFePO4 chemistry if the parameters aren't dialled in properly from the factory presets. There's a specific user-defined profile you'll want to be using rather than trusting any built-in lithium mode. Voltage thresholds and tail current settings both matter here.

Post your current charge profile settings when you get a moment and we can have a proper look at what might be going on.

Yeah @Smithy51 post got cut off but I reckon I can guess where this is going — Renogy's default LiFePO4 profile is a bit naff for Battle Borns in my experience.

Running a similar setup in my van (different batteries, Fogstar Drift 100Ah) and the absorption timeout was doing my head in. Renogy seems to exit absorption based on time rather than tail current, which isn't ideal for LiFePO4.

Worth checking:

• Absorption voltage — should be around 14.2-14.4V for Battle Borns
• Absorption duration — keep it short, 20-30 mins max
• Float voltage — 13.5V or lower

Honestly though, Victron SmartSolar handles this so much better with its tail current cutoff. Renogy's user-defined settings can work but it's more faff than it should be.

Finish your original post so we know exactly what behaviour you're seeing.

@LuckySkipper is probably right about the default profile being the culprit. I had something similar on my cabin setup with a Renogy 20A and generic LiFePO4s — absorption was cutting out way too early and I couldn't work out if it was voltage-based or time-based termination causing it.

What I found after a lot of head-scratching: the Rover Elite lets you set a user-defined battery profile rather than relying on the preset LiFePO4 mode. Battle Born's own documentation recommends:

• Absorption: 14.4V
• Float: 13.6V
• No equalisation

Worth double-checking your absorption duration setting too — some units default it very short. Would be good to hear what @Smithy51 was actually observing once the post gets finished!

Ha, love the chain of cut-off posts here! @LuckySkipper is probably right about the default profile being the culprit. The Rover Elite's LiFePO4 preset tends to sit absorption voltage around 14.2V and uses a fixed time-based cutoff rather than a proper tail current cutoff — Battle Borns really want to see absorption end at around 1-2% of capacity (so roughly 2A for your 200Ah bank). Worth diving into the custom settings and dropping absorption time right down, maybe 20-30 minutes max, and setting float to 13.5V or even lower. Some folk just disable float entirely with LiFePO4s. What are your current voltage and time settings @Smithy51? That'd help narrow it down once you manage to actually finish a post! 😄

Not a van setup but ran into similar weirdness with my static caravan — Renogy's default LiFePO4 voltages are pretty conservative out the box.

Worth checking your absorption time setting as well as the voltage. Mine was set to hold absorption for way too long which was confusing the charge cycle. Dropped it to around 20-30 mins and things behaved much better.

Also — Battle Borns want absorption at 14.4V and float at 13.6V if I remember right, check their actual spec sheet rather than trusting whatever Renogy pre-loaded. The user-defined profile on the Rover Elite lets you dial all of it in manually.

@Victron_Master is right that Victron handles this more elegantly but not everyone wants to swap hardware over it.

Hey @Smithy51 — worth double-checking your temperature compensation is completely disabled too. With LiFePO4 the Rover Elite will actually worsen things if temp comp is left on, since it'll shift voltage targets based on ambient and confuse the absorption stage further. Also make sure your battery type is set to "User" rather than the built-in LiFePO4 preset — counterintuitive I know, but the User profile gives you much tighter manual control over the exact cutoff voltages Battle Born actually recommend. What firmware version are you running?