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Which battery chemistry is best for your RV – Lithium or AGM?

WORDS BY JOSEPH VAN WOERKOM PHOTOPGRAPHY BY JOSEPH VAN WOERKOM AND CARAVAN & MOTORHOME

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If you’re in the market for a new RV or simply looking to replace the house battery, what type of battery should you use? There are now two main types to consider, AGM and lithium – specifically LiFePO4.

Most people would know that you need a deep cycle rather than a starter battery for RV use but unfortunately there are many different battery chemistries to choose from. For the sake of this article we’ll restrict ourselves to two types; AGM lead acid and lithium (specifically LiFePO4).

AGM batteries have a lot of advantages compared to traditional wet cell lead acid deep cycle batteries including being maintenance free, virtually spill proof, and has faster recharge times. AC & DC chargers for AGM batteries are readily available and at reasonable cost.

Lithium batteries are the new kid on the block and are much more expensive than AGM batteries for the same Amp-hour (Ah) capacity.

They are smaller and much lighter than AGM batteries for the same Ah capacity and can be repeatedly discharged to a much greater extent without suffering any ill effects. Because they can operate at a much lower State of Charge (SOC), lithium batteries need less overall Ah capacity to reliably deliver the same amount of energy compared to AGM batteries.

Lithium batteries can also be recharged much more quickly than AGM batteries, even with identically rated chargers. This is because lithium batteries have a much lower internal resistance and therefore can accept higher charging currents. Also the terminal voltage of lithium batteries does not rise significantly while being charged which means that full charging current can be maintained right up until the battery is fully charged.

Sound good, don’t they? But what are the disadvantages?

Well, apart from the significantly higher purchase price, lithium batteries also require a Battery Management System (BMS) in addition to the charger to ensure that the cells within the battery remain balanced (have the same SOC) and to prevent both over charging and over discharging. Any of these situations can lead to rapid and complete battery failure.

Also, you may need to get a new battery charger as your existing AGM battery charger might be incompatible with lithium batteries.

In my opinion, lithium batteries may make sense if you are purchasing a new RV, use your RV a lot (more than a few months each year) and have high electrical demands (like running compressor fridges and air conditioning from batteries). The size and weight reduction and faster recharging they bring might also be important for some people.

If however you are simply replacing worn out batteries in an existing RV, don’t use your RV a lot or have modest electrical demands, I think it would be difficult to justify the significant additional costs over a traditional AGM based system.

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