How long will it last? – caravan lithium battery put to the real-life test

They say that lithium batteries would outperform AGMs in RV applications, but can we compare apples to apples and find out how long a caravan lithium battery would last in a real-life application?

Last updated: 28/10/2020

Lead acid batteries in RV applications

Lead acid batteries in deep cycle applications are highly popular with RVers, allowing them to have access to 12V power wherever they are. Depending on the technology (AGM, Gel), and quality of a lead acid battery, their prices vary from $200 to $1000.

Deep cycle batteries are designed to cycle (discharge and recharge) multiple times, but their life span depends on how they are treated. Degradation of the internal lead plates causes aging of the batteries, which is caused over time, but most importantly, by exposure to high discharge currents. This in practise means that for their longevity lead acid batteries should not be discharged lower than to 50% of their capacity.

How to use lead acid batteries?

In the ideal usage when a lead acid battery is discharged to 70% of their remaining capacity, they could offer the user over 1000 cycles, but would not provide much power in this scenario. Thus, a 100Ah battery would only provide for 30Ah power, which could only cover the basic power needs such as usage of energy efficient lights and watching TV for an hour, before you need to recharge your battery.

It is recommended to discharge a lead acid battery to 50% only, which would give the owner 400-500 cycles at best and 50Ah of energy. However, when you are out in the field, free camping, it is not always possible to stick to the ideal scenario. Most RV travellers would confess discharging their battery down to 20%, which cuts the lifespan of the battery dramatically. 150 cycles is all you would get from a deep cycle battery subjected to deep discharge.

Caravan lithium battery tested at BMPRO

Lithium batteries, on the other hand, can be discharged much deeper and their capacity is 60% greater than of a lead acid, which means the same size battery gives you much more power and allows to enjoy free camping in comfort.

Lithium batteries are absolutely safe to discharge down to 2% (which is 98% depth of discharge (DoD), and there are no corrosion prone materials inside. However, this is all in theory, and the cycle life of the LiFePO4 batteries claimed by manufacturers is often based on the calculations, simulations and projections based on the ideal test of a single battery cell.

At BMPRO, we decided to put an Invicta LiFePO4 battery to a real test to check how many cycles would it run when cycled through 98% DoD and full charge. Unlike many tests held on the cell level, we have been testing the complete battery.

Real life test setup

The test started on the 14th of November 2017 using Chroma regenerative battery pack test system model 17020 which stimulates real world scenarios of battery usage. The Invicta caravan lithium battery has been connected to a Chroma tester which discharged it to 2% of its initial capacity (100Ah) and then recharged back to a 100% with a lithium compatible BMPRO battery charger. With roughly two cycles per day, the battery has been treated in this regime non-stop since the onset of the experiment. The temperature on the factory floor is not stable, and at nights or during holidays, with no heating or cooling in operation, can vary from 8°C to 40°C, so the test is very close to the real life conditions.

As a result, we got the battery discharge curve showing the decline of the full battery capacity with the quantity of cycles run. As you can see from the graph, the initial capacity was slightly higher than nominated (105Ah), and two and a half years later, it is still a fully functional battery with marginally reduced capacity (around 85 Ahr).

A lead acid battery treated in the same regime would die after ca. 200 cycles, which means this LiFePO4 battery would have already outlived 7 AGMs. In dollar value, it would already recover the initial investment, as well.

What’s next?

The experiment is going on – we are updating the counter below every week so that you could follow the story of an Invicta caravan lithium battery further. So far, it is still running its marathon.

Start date: 14/11/2017
Depth of discharge: 98%
Cycles per day: 2
Last updated: 28/10/2020
Days in operation: 1079
Cycles run: 2309
Current capacity: 82 Ah

… and still going

caravan lithium battery put to real life test
Capacity vs number of cycles of LiFePO4 deep cycle battery
Why Lithium? It is a numbers game
High Amp Battery Management System BatteryPlus35HA
Is your caravan Lithium-ready? Use BatteryPlus35HA or J35D - Lithium compatible caravan power management systems by BMPRO

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6 thoughts on “How long will it last? – caravan lithium battery put to the real-life test”

  1. Would hace been good to see a agm tested side by side at the same time to see real result instead of “would have outlaster 7 agms”.
    Just saying.

  2. must be a poor quality agm your testing and comparing to, put your money where your mouth is and fit your lithiums into my van and i will do a true test for you as we live in ours running coffee machine , microwave, washing machine, computer on charge most of the day as my wife works from van, charging internet phones, running lights, pump and all 12v needs. I got 7.5 years out of quality agms and now them same batteries are running a car winch on a car trailer for 12 mths now , so been 8.5 years on a agm more cycles then your claiming. Do you want to put yours to the test contact me

    1. Hi Rod,
      You are right, if good quality AGMs are used correctly and are never over-discharged, they last considerably longer. According to the Battery University, if AGM’s Depth of Discharge is no lower than 30% it could run over 1000 cycles. However, in our test lithium batteries undergo Depth of Discharge of 90% and have done over 2000 cycles. No AGM battery would survive this test.

    2. True enough. The 50% rule for AGM is a myth. In reality they can be discharged much further. The folly happens because people get misled by the term cycle count. It doesn’t take a huge brain to see that if i discharged a battery to 40% rather than 80% I’d require double the number of cycles for the same energy output. Funny how people don’t work this one out for themselves.

  3. Hi – Quick question. When doing this test, how do you know when you have depleted 98% of the battery capacity?

    1. Hi, we are discharging the battery down to 11.5V which according to the manufacturer means it is down to the required remaining state of charge.

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