How To

How to Charge Lithium Ion Battery?

Lithium (LiFePO4) batteries are unbeatable when it comes to cycle stability, performance and energy density. To keep the joy of the power packs for a long time, lithium batteries should be charged appropriately and stored. Again and again, however, questions arise on how to correctly charge lithium-iron-phosphate batteries and save them properly between the free home tours.

Lithium batteries do not want to be full! Or is it?

In the early days of lithium technology in motor homes, no one has cared for the right care. Even the suppliers of motorhome lithium batteries were no cause for concern. 
It is known that lithium batteries will not be damaged if they are not fully charged. Whether a permanent state of charge of 100% for the cells with lithium technology is conducive to life or instead has a negative effect, may not be evident to this day.

The characteristic curves of the manufacturer’s chargers indicate in any case that a permanent full charge of the batteries is not a problem. Some even recommend a storage/charge retention voltage of 13.5V, which corresponds to almost 100% state of charge. If importers are questioned about LiFePO4 cells, storage at 13.2-13.3V is recommended. So we are fishing in the murky and there remains only an analysis of the swarming knowledge:

  • All lithium batteries are similar in their properties. Whether Li-Ion, Li-Po or LFP, as used in motorhomes. Different chemical compositions improve the features of the cells, or they become safer, as is the case with LiFe (Y) PO4.
  • The batteries do not harm a medium state of charge for a long time! Everyone agrees. Whether the batteries are allowed to be entirely stored, nobody says so clearly. Wikipedia writes, “do not fully stock,” importers of Winston cells also recommend rather 13.3V instead of full.

So there is a trend to see that it does not seem to be better to store the batteries adequately. At least this storage does not damage the cells!

So I suppose that a LiFePO4 and LiFeYPO4 battery feels most comfortable with 50% state of charge. Everything above and below does not extend the life expectancy.

But attention

Nevertheless, it remains a battery that is charged and then discharged again. Lithium batteries can do that much better than the lead-acid batteries used in the past. Just with the small difference that lead-acid batteries should always be full and lithium batteries should always be half complete – to achieve the same optimal life expectancy.

So I will always fully charge my battery if I want to use the full capacity. But I will also spare the cells by not fully charging them in the summer when there is more than enough power available anyway.

Only 50% charge state with lithium batteries?

What consequences does this have for the use in the motorhome?

Again and again, customers ask me: “But if the battery should ideally only be kept at 50%, then yes, I can not use the capacity …”
Well, the same applies to the lead-acid battery with 100% – still unload it to power off to have the outlet – right?

A small example: If you do not drive, a car tire will last a lot longer – but people still drive it and accept the wear and tear. If you drive with the tire in Formula 1, he has left after a few kilometers. If you push ahead of time and slow down a bit in the bends, car tires will last much longer. 
The same applies to lithium batteries: If you use only 70% of the capacity, there are 5-7000 charging cycles in it – if you use the full size, there are only 1000 cycles left. Both numbers are still many times the expected life expectancy of lead acid batteries.

Why should a lithium battery not always be full?

I’m not a chemist, but a hands-on user, using all sorts of sources and trying to knit a practical solution for the end user. Unfortunately, many manufacturers provide substantiated information – neither about the operation nor storage of the batteries. Even suitable chargers, which offer a storage mode for lithium batteries, there are still few. Taking the average of all opinions, including battery manufacturers like Winston, the result is:

When charging a lithium battery, the pressure in the cell increases with increasing voltage. High voltages, i.e., top charge states, ensure faster aging in the battery and ultimately premature loss of capacity. 
The less long the battery is kept at 100% charge, the better it is for the lithium cells. There is nothing wrong with charging the battery fully while riding the booster and then powering the motorhome for a few days without recharging. A week’s camping holidays at the campsite with connected shore power and switched-on charger, however, are less optimal.

Laptops, e-cars, etc. should not be fully stocked

That lithium batteries should not always be stored fully charged has already been recognized in other industries. Here are a few examples that come to my mind:

  • Laptop Batteries: Lenovo has individual charging profiles that charge the battery only to a certain percentage; for instance, if you do not always want to use full capacity. If the battery is operated on the mains for a long time, it can be set so that the battery is only kept at 50% charge level. This should significantly extend the life of the cells, according to Lenovo.
  • E-bikes: Also, some manufacturers point out that the batteries should not be stored entirely in winter.
  • E-cars – certainly not without reason, the manufacturers take the trouble to develop appropriate controls that allow the user to determine the time of full charge of the battery. With Tesla, one can adjust by App, how full the accumulator should be at a specific departure time. The car then calculates the charging current so that exactly at the time the desired state of charge is reached. This prevents the battery from being kept unnecessarily long at 100% charge level.

All this effort would not be necessary if it would be safe to store the battery to 100% full. Because power weighs nothing, so it would not be a disadvantage for the user, if you always had a whole array, even if you do not need it. 
Also, Wikipedia writes that it is a full charge, in addition to high temperatures, the battery life is not beneficial.

So I’m trying to keep my lithium batteries between 10% and 90% charge level – with my power consumption that’s no problem from fall to spring. 
Since I use the batteries every day, storage is less of an issue for me, but in summer, the solar system delivers so much energy that the lithium batteries are already fully charged in the morning. This has made me think and I started to look for a solution.

Control the state of charge of the lithium battery itself.

I figured it would be easiest if you did not fully charge the battery if you did not need the full capacity anyway. For example, during the summer holidays, where the solar system provides a lot of energy and is often consumed only a little. Switching off the solar system would be a way – but it means that the battery would be discharged during the day again, which means unnecessary wear because solar power is cheaper than lithium electricity. So there has to be a way to teach the solar controller to gently charge the battery without always charging it to 100%. 
This function would also be useful if the motorhome is unused at home in the sun and no power is consumed.

Solution: Programmable solar charge controller

Victron Energy’s MPPT solar charge controllers can be easily customized with a self-made charging curve to achieve a thedesired mode of operation described above. 
To achieve this, you set the charge curve on the solar charge controller so that the battery can not be fully charged, even if the sun would shine around the clock.

The same goes with a 230V charger if the motorhome under the carport cannot be supplied with solar power. To protect the battery from uncontrolled over-discharging by the self-consumption of BMS and other miniature consumers, the system must either be completely switched off, or you connect a shore power charger, which keeps the battery permanently in an ideal state of charge by a first charging voltage.

Hach is the one effort now thinks so many. I would say, to have to be on the lookout for a power outlet while vacationing would be much harder for me than switching over a charge curve on a charger every few days or weeks.

Charging with solar power – that’s how it works

The Smart Solar MPPT Charge Controller Victron Energy can be programmed via app pretty easy. This is possible with any Victron Energy SmartSolar MPPT charge controller or with the BlueSolar MPPT charge controllers with new Bluetooth dongle. 
I have created and saved three charging characteristics. Depending on the desired operating mode, I can give the controller the right profile in seconds.

I have put together three characteristics, which I can call just as you wish.

  • Full performance (100% SOC)
  • Summer operation (about 80-90% SOC
  • Storage mode (50% SOC)

The following parameters are stored in the charge controller:

Power mode – always full for bad weather

Here the battery is charged according to the Victron recommended charging curve. For normal operation, this is ok, if always the full capacity is needed. When I see bad weather looming, I activate this profile the day before so that I have the full battery capacity for the bad weather period.

Setting values ​​for the MPPT controller:

  • Constant voltage 14.2V
  • Maximum constant voltage duration 6 hours
  • Maintenance voltage 13.5V
  • Compensation voltage 0V
  • Automatic cell balancing disabled

Summer operation – no full charge

So that the lithium battery does not stand around every day, I lower the constant voltage and maintenance voltage slightly. For this, I activate the cell balance for every 30 days with 14.4V. 
This setting corresponds to about 90% charge level. However, whether the 90% are achieved, depends on how empty the battery was in the morning. Due to the low constant voltage, the maximum charging current breaks down sooner and it takes some time until 90% is reached. Here you can also play something, I put the constant voltage in the summer partially down to 13.7V, if I have more than enough solar power anyway.

Setting values ​​for the MPPT controller:

  • Constant voltage 13.6-14V
  • Maximum continuous voltage duration of 6 hours
  • Maintenance voltage 13.4V
  • Compensation voltage 14.2V (Victron to 2018 14.4V)
  • Automatic cell balancing every 30 days

Storage mode – steady state of about 50%

If the motorhome is not used and is in front of the house in the sun, the storage mode for charge retention at about 50-70% charge state. For the lithium battery that is much more relaxed than when it gets anew on the cap every day with 14.2V.

Setting values ​​for the MPPT controller:

  • Constant voltage 13.15-13.35V
  • Maximum continuous voltage duration of 6 hours
  • Maintenance voltage 13.15-13.35V
  • Compensation voltage 14.2V (Victron to 2018 14.4V)
  • Automatic cell balancing DISABLED

Risks when storing lithium batteries in the motorhome

The following problem concerns us when operating lithium batteries. Although the cells themselves have an extremely low self-discharge, this is negated by the power consumption of the monitoring electronics again. Therefore, lithium systems discharge over time anyway. 
Who now thinks that such a LiFePO4 battery can be put down, and you do not have to worry about it, because the BMS protects from deep discharge, that may have to pay dearly:
In operation, the BMS reliably shuts down the loads during deep discharge and when the battery is recharged, everything is in the green zone. However, if the system discharges unattended due to self-consumption, the BMS also switches off on day X because the battery is empty, but the self-consumption of BMS, battery computer and cell balancers in the battery continue to cause a discharge until the battery dies!

Therefore, when storing lithium batteries, make sure that the system discharges as slowly as possible when not in use. (This can be achieved by disconnecting the battery from the BMS and battery computer via a battery disconnect switch.) 
Or making sure that the battery does not fall under a particular state of charge, as described above, by charging the chargers set voltage.

To prevent uncontrolled discharging of the LFP battery, there are now three ways:

  1. To be on the safe side:
    Disconnect the battery directly at the pole from all consumers. Victron Energy LiFePO4 batteries have a BMS in the negative lead. If you disconnect the negative lead directly from the battery post at SOC 80%, the battery is safe and can be stored for one year without having to be recharged. If you do not feel like looking for the tool every time, or if you struggle to get to the battery pole, you install a circuit breaker, which is connected directly to the battery post and before the BMS. Not to be confused with the disconnect switch in the camper. The only switches off the 12V consumers, but not the BMS. 
    Without the small consumers, an 80% full lithium battery can be stored for one year. The 200AH LiFeYPO4Fraron battery has integrated the BMS. Although the consumers can be switched off externally via the main switch, the internal consumption through BMS and balancer remains. Farron, therefore, recommends switching off the battery at 100% charge and recharging it every six months.
  2. Always on shore power:
    If the vehicle can be connected to the shore power, there is another way to keep the battery always at about 40-50% state of charge. The chargers BLG20 to BLG50 from my shop have a power supply mode in which only a fixed voltage is output, without characteristic. This voltage can be adjusted via a switch. (See below)
  3. Storage mode via the solar system: Parallel to shore power, there is still the option of moving the solar charge controller to the storage mode described above. Then the battery is always recharged even without shore power connection – as long as not for weeks snow or leaves of trees on the solar modules. Next, make sure that the motorhome is not in the shade.

Lithium storage mode with the 230V charger

Most chargers in the camper load with 14.4V Ladeendspannung and then keep the batteries at 13.8V. For lithium batteries are 13.8V in the long run too much. The cells are under high pressure, which is detrimental to life. It is, therefore, better if the battery is not used, either disconnect it or protect it against unwanted discharge with low voltage. This charger is easy to implement with this charger. You can order the charger conveniently directly in my shop.

The Power Supply function, with 13.2-13.3V constant voltage, is the perfect storage mode for lithium batteries! It is not charged, but only prevents the voltage drops below 13.2V. The battery cannot be discharged too deeply.

As you can see in the picture above, the BLG Series 3 chargers have small slide switches (number ➊ / ➋ / ➌ in the picture).

Switch ➋ (battery type) is set once to WET / best AGM battery and then not changed! With the switches to the right of it, we tinker us two characteristics for the storage mode and regular operation:

The proper service, full charge of the battery:

  • Switch ➋ WET / AGM
  • Switch ➌ 13.5V

storage mode

  • Switch ➋ WET / AGM
  • Switch ➌ 13,2V
  • Switch ➊ POWER SUPPLY

My recommendation: loading and storage mode without switching

At this setting, the charger first charges the battery fully and performs cell balancing. After that, the charge sustaining voltage drops to 13.2V, which causes the state of charge to settle by 50%. In this position, the charger can remain on the grid for any length of time.

  • Switch ➋ WET / AGM
  • Switch ➌ 13,2V

When the next journey begins, unplug the shore power cable and the charge booster will recharge the battery while driving. Alternatively, you can also switch the charger a day before, so that the battery can be fully charged overnight.

Why do you have to recharge lithium batteries occasionally?

Now it is so that the cells in the LFP battery drift slowly over time and have different states of charge. Therefore I recommend during the usage time to recharge the battery once every four weeks so that the balancers can balance the cells. It does not matter now if it’s for 4 or 6 weeks. The battery will not hurt if more weeks pass. If the battery is not used for an extended period, there is no need to balance. You can also read our trolling motor battery reviews to choose the best one for your boat. 


For 5-6 years, lithium LiFeYPO4 batteries are already installed in motorhomes. A retrofitting of the established charging technology is not necessary if the chargers can be set to a charging characteristic for wet lead batteries (Lead Accid / WET / lead wet). If the motorhome is not used for a more extended period, the battery will be disconnected from the electrical system and BMS at about 80% state of charge and can then be stored for one year.

But this is too complicated for many users, especially since then the car radio and the clock have to be readjusted. Some customers also want to be able to use their motor home spontaneously or leave it connected to the shore power during the winter so that the heating system can run through. Here then the conversion to a suitable charger makes sense so that the battery can be kept by shore power in the ideal state of charge and discharge can be prevented.

The same applies to the solar system – if the motorhome is ready for use the whole year outside – then a solar charge controller should be retrofitted, which does not charge the battery every day to 100%. If the LiFePO4 battery is only “stored” via solar, care must be taken, especially in winter, that there is no accidental over-discharge in the event of snow on the motorhome roof, because the solar system can not supply any power for a long time.

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