12V Guru – Can I connect lithium ion batteries in parallel?

Question to 12V Guru

We have heard stories about lithium and their benefits and reckon we want to go ahead but not sure that a single 100A will be enough as we get off into the bush a bit.  What are your thoughts installing two batteries as I have heard conflicting stories about paralleling lithiums?

Davis Earle, Port Augusta, SA

12V Guru answers:

Thanks, Davis, for your question – certainly lithium batteries are now more and more of a hot topic as RVers opt for a solution that saves them so much weight, gives greater off-grid capabilities, charge in less than half the time and more.  Get past the price and you will be winning and grinning into the future as you don’t need to replace those boat anchors known as lead acid batteries!

Do I need one or two lithium batteries?

The first issue you raise is the need for one or two batteries.  I guess this issue will arise regardless of whether you are using lead acid or Lithium batteries.  To answer this accurately there are two parts – firstly you probably need to really be able to understand your energy requirements when you do decide to travel off the bitumen. Is there an opportunity not to use energy hungry devices for a few days such as the microwave or the coffee machine? Admittedly the latter would be hard for most of us! Secondly, you will need to be able to guestimate what you believe you can generate in power to replenish the batteries – generator, solar or dc-dc?  Once you have this understanding, probably through experience, you will be able to understand if you need more than one battery.

The big thing to remember though is that with lead acid batteries you would normally only discharge these down to 50% remaining capacity effectively only giving you 50Ahr of energy from a standard 100Ahr battery however with a Lithium battery it is perfectly fine to discharge lower to around 20% remaining capacity so this will give you approximately 80Ahr of energy – a 60% difference. Once you increase the number of batteries installed than this additional differential obvious also increases and becomes substantial.

Can I safely parallel lithium ion batteries?

Regarding the second part of your question on connecting lithium ion batteries in parallel your answer is totally dependent upon the battery and the battery management system that is built into the battery.  Not all lithium batteries are created equal – especially cheaper batteries.  For example, the BMPRO Sentry lithium batteries are capable of being installed in parallel with up to 4 batteries.  As per good practice with lead acid setups all batteries should be of the same brand, size and age.

Check with your battery manufacturer first. If they advise it is possible there are a few simple rules to follow to successfully be able to enjoy what may seem like endless power:

  1. When setting up the system ensure that all batteries have been individually fully charged and have an Open Circuit Voltage (this is the measure of energy potential between the positive and negative) after being rested (not on charge for at least 1 hour) and with no loads connected within 0.2V of each other.
  2. Ensure you are using wiring that can carry higher amperage.  Remember by paralleling the batteries you have kept the nominal voltage the same at 12V but increased the Ahr capacity and therefore the discharge and charge will be higher.  Good wiring practice also means drop a fuse in on the anode (positive) side.  Keep the length of the wiring between the batteries consistent. If you have one or two cables longer than others it changes the resistance within the pack of batteries.
  3. Double check all positives are connected together and all negatives the same – do not under any circumstances reverse the polarity and never series a parallel bank of batteries.
  4. Lastly, every three months ensure the new pack is fully recharged and remember that if you need to replace one battery in the pack than you will need to replace all batteries.

Lithium batteries are an investment and can offer substantial benefits longer term and for extended off-grid camping providing proper maintenance and care is maintained.

Safe travels – 12V Guru!

The article is written for Caravan World Magazine.

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