How to lose weight instantly! Ditch AGM and choose LifePo4

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We finally took the plunge and replaced our lead-acid motorhome battery with a shiny new lithium one. Read on to see how even though it may not be a game changer, it certainly made life better.


Towards the end of our motorhome trip last December, we were running out of electrical power. A combination of shorter days generating less solar power and needing to run the diesel heater, we found it necessary to switch off the compressor fridge to save energy. The fridge uses the most power so is an easy way to save power, but at the risk of spoiling all your food. Even worse, you could end up with warm beers!

Our leisure battery was a 100AH AGM, so not very big by motorhome standards, and it was obvious the time had come to increase our capacity.


Our motorhome actually has room for a second battery under the floor next to the first one. The most straight forward option would be to stick a second 100AH AGM battery and wire it in parallel with the first. This would double our capacity quite simply.

Or we could replace the AGM battery with a new LiFePo4 lithium battery. This is what we went for in the end. But firstly, it might be useful to have a list of the good and bad points of lithium batteries….

Advantages of LifePo4 vs Lead-Acid

  • Lighter – Our AGM battery was 27Kg, this was replaced with a 10Kg LifePo4 battery. Nearly 1/3 of the weight of the lead battery!
  • Discharge amount – A lead battery can only be discharged about 50% of its capacity otherwise it will get damaged. A LifePo4 battery can be discharged to 80% and depending on who you believe even 90%. This means that a 100Ah lead battery actually only has 50Ah of usable capacity, compared to a 100Ah lithium battery that has at least 80Ah of capacity. In plain English it means you can run your stuff for longer before it needs charging!
  • Longer lifespan – A lead battery is only good for a few years, and then the capacity falls away sharply. A well-treated lithium battery can last ten years and thousands of charging cycles.
  • Faster charging – Lithium batteries can cope with higher charging currents, if your charger supports that kind of thing.
  • Maintenance free – You plug it in, and forget about it. Nothing else needs doing!
  • Stable voltage – Have you ever noticed how at night when all the lights are on in your motorhome, and someone turns on a tap or the fridge jumps into life how the lights dim slightly. It is just for a second, and it is something you get used to. When you have lithium, there is no dimming at all. The voltage of the battery stays constant until it has nearly ran out of juice.

Disadvantages of LifePo4 vs Lead-Acid

  • Cost – Although this is not that great now. I will tell you in the next section what we paid.
  • New chargers – Depending on what you have in your motorhome already, you may need to replace your battery chargers.
  • Need to configure charger to different voltages/profiles to get the best out of lithium and prevent damage from overcharging.
  • More sensitive to temperature – You cannot charge a Lifepo4 battery below 0C without damaging it, so it is important to protect it from frosty temperatures.

What we did and what it cost

We had been watching the price of Lifepo4 batteries falling steadily all through 2023. By the January 2024 sales, Amazon had no-name 100Ah LifePo4 batteries for less than €250. A decent, new AGM battery is nearly €200 so we figured it was finally worth taking the plunge and going lithium. Being from Amazon, I could send it back if it was a load of rubbish.

The battery arrived and was physically about the size of the old one, but WAY light. I could pick it up by its carry handle with one finger! The lead battery would break my finger if I tried that!

Our battery box lives below the floor level in the motorhome, so is exposed to the outside temperature. Plus there are holes to allow gas to escape when charging a lead-acid battery. I figured before I fitted the new battery I should protect it from temperature extremes. To do this I blocked the ventilation holes, and lined the box with a decent amount of insulation foam. Hopefully will protect it from getting too cold in winter, or too hot in the Spanish summer!

I also, reconfigured our Victron Smart Solar charger so that the absorption voltage was 14.6V, and the float voltage was 13.5V. This was all from the battery datasheet provided.

The final change I made was on the shore power (electric hook up) charger. Our van is 20 years old, so this charger is pretty stupid. It just puts out 14.4V continuously when on electric hook up. Over a long time, if plugged in, this voltage could damage the battery. Lots of chargers have some way of changing this to a lower voltage. On our charger there was a recessed switch you could change with a flat-head screwdriver. I set this to the other setting of 13.5V, figuring that although this would not charge it properly if flat, it would prevent damage and put some energy in. We do not use electric hook up much, although on our last trip we managed to get two days of free electric and the charger and battery worked fine with this setting.

How did we get on

In short, really well! We were able to leave the fridge on 24 hours, so the milk was still cold in the morning. Also, with the lovely sunny days we have in winter in Spain, the Victron charger was able to recharge everything by lunchtime.

Another thing I noticed, the battery charged quicker than before. Whether it was the sun, or driving along the battery seemed to accept the charge better.


By replacing our lead battery with lithium we got more capacity – at least 30Ah more, for something that weighs 17kg less, and should last a long time!
Now that the price difference between AGM and LifePo4 is so small, I do not think there is any debate now. I would always choose LifePo4.

Please check out our trip last month to Andalusia where we tested the LifePo4 battery for a couple of weeks. Spoiler – The battery did not miss a beat!

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