At Xantrex, our tech support team receives many questions from RVers and boaters regarding lithium installations. This article addresses some of the top questions regarding compatibility of different battery setups from our tech support team member, Shaun.
Q: Can I use 2 lithium batteries of different sizes in the same power system? (assume same chemistry and brand)
A: This is technically possible if we assume that the nominal voltage for each battery is the same (i.e. don’t mix a 12-volt battery with a 24-volt battery). However, your electrical loads will be drawing power from both batteries equally. This means that the smaller of the two batteries will hit its depth-of-discharge point and drop into a protection mode well before the larger of the two batteries. If the battery is not reactivated and charged within a few hours, it could be damaged beyond repair. The operator might not even be aware that the battery is in a fault (or protection mode) as the larger of the two batteries will remain functional.
Therefore, we do not recommend that you use 2 lithium batteries of different sizes in the same power system.
Q: Can I add a Xantrex Lithium to my existing lithium power system that is already using another battery brand?
A: This will technically work if we assume that the nominal voltage for each battery is the same (i.e. don’t mix a 12-volt battery with a 24-volt battery). However, it will be difficult to predict if the resistance of the BMS and the capacity of the cells will result in an even drain on the batteries, as they may function in a slightly different way. This can easily result in one battery dropping into a fault/protection mode well before the other batteries in the bank. It is recommended that you use identical batteries connected with identical gauge and length of cables. This will minimize any issues of charging and discharging between the batteries.
We strongly recommend that all the batteries in your power system are the same brand and size.
Q: Can I add a Xantrex Lithium battery to my existing non Lithium power system?
This will technically work if we assume that the nominal voltage for each battery is the same (i.e. don’t mix a 12-volt battery with a 24-volt battery). However, the actual fully-charged voltage of different battery chemistries will end up conflicting with each other. For example, a 12-volt lead-acid battery will be fully charged when its resting voltage is somewhere between 12.6 and 12.8 volts, where a LFP battery will usually be between 13.8 and 14.1 volts. If we connect the two batteries together, there will be a constant low-level drain from the LFP battery into the Lead-Acid battery as they try to balance the voltage. The Lead-Acid battery will bleed off this power as slightly higher heat.
In summary, we recommend that you do not add a lithium battery to your non-lithium power system.