Hi, Dave,
Last summer I replaced my two lead acid batteries in my trailer with two 100-amp LiTime self-heating Bluetooth-enabled batteries, wired in parallel. I have 400w of solar on the roof, and this setup has worked very well for us dry camping. I’ve noticed, though, that instead of both batteries drawing down approximately equally, one will draw down and the other stays at 100%.
I did consult with LiTime and this is the response that I got, although it still seems to me that at some point the second battery should also be drawing down. I have done their procedure and it works, but seems cumbersome. The initial battery that draws down has never fallen below 60%, so I don’t know if the second battery would eventually start drawing down.
LiTime uneven charging response:
The reason this battery system discharges sequentially is because the voltages at the terminals of the two batteries are different. The battery with the higher voltage takes on all the discharge current first.
Once the voltage of the higher voltage battery drops due to discharge and reaches the same voltage as the battery next to it, the two batteries can discharge together.
This is a normal discharge phenomenon for series-parallel batteries.
Solution:
(1) Temporarily turn off the discharge of the battery that is discharging, then resume the discharge of the battery.
(2) Connect the load discharge current ≥50A.
Online Sales & Consulting (OSC) Department
Many thanks. —Warren, 2024 Grand Design AIM 15RB
Hi, Warren,
If your batteries are connected parallel, positive to positive/negative to negative, they create a 12-volt “bank” which doubles the amp hours but should be sensed as one power source and drained evenly.
Recommendation from Battle Born® Batteries
So, I sent your question to the tech guys at Battle Born® Batteries and got the following response:
This can occur with other batteries as well, particularly if the load is being drawn primarily from one battery in the battery string. Another common cause is when the batteries are not completing a full absorption charge cycle, which is necessary to properly balance the cells. When the cells become unbalanced, you may notice a difference in load output between the batteries.
For our systems, we recommend charging each battery individually through a complete absorption cycle before connecting them together. We also recommend connecting the system so that the positive lead is taken from Battery 1 and the negative lead is taken from Battery 2. This ensures that both the charging current and the system load are distributed evenly across both batteries.
As part of regular maintenance, we recommend disconnecting the batteries once a year and charging each one individually through a full absorption cycle. This helps keep the cells balanced and ensures the batteries continue to perform at their best.
They also indicated that this could happen with lithium batteries that do not use the cylindrical cells, rather prismatic or pouch cells. The challenge with many inexpensive lithium batteries is we can’t see what is inside so there is no way to tell.
Do an annual “full absorption charge”
What I did find interesting was the recommendation to disconnect the batteries once a year and do a full absorption charge. I had never heard that before and don’t think most RV owners that have lithium batteries know this either.
Battle Born stated that if your converter/charger has a lithium setting or can be customized for the specific charge profile, it will work. They recommend the Victron IP65, which is a Blue Smart charger and is fairly inexpensive. You can find it on the Battle Born site here. Make sure you get the 15A version, as there are others that are strictly trickle chargers.
More posts from Dave on lithium batteries
- I want to switch to lithium batteries, but I have some questions
- Switching to 600Ah lithium batteries. Is 200W solar panel sufficient?
- Should I upgrade RV house battery system to 48-volt for boondocking?
- Can different type and age RV batteries be mixed? Can I add a lithium battery?
- My RV’s “larger” batteries are dead. Can I replace them with lithium?
- Will RV’s house batteries ‘play nice together’ if I replace chassis battery with lithium?
- Will my RV’s charger be sufficient for new lithium batteries?
DAVE HAS ANSWERED MORE THAN 1,200 readers’ maintenance and repair questions. Read a directory here. There is so much to learn!
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
HAVE A QUESTION FOR DAVE?
Send your inquiries to him using the form below.
RVDT2955
LiTime’s app isn’t accurate anyway. It does not show the small reductions in amp hours due to draw downs by propane monitors, etc. It will show the batteries as fully charged when in fact they are not.
We added a Victron Smart BMV-712 which shows the actual SOC.
This is harder than Japanese arithmetic. I’m glad I only run one lead acid battery.
Thank you, Dave. The batteries are wired in parallel in the way that BattleBorn recommended. I will try the method of charging them individually as BattleBorn recommended. When I remove them for the winter I run them down to around 50% for storage, but haven’t been individually fully charging them before reinstalling them. Greatly appreciated!