When setting up battery characteristics on the MultiPlus-II, selecting “Lithium” greys out the selection for “storage mode”. Why?
Lithium batteries don’t need storage mode. They don’t hardly self discharge and its not good for them to have a constant charge voltage when they are already fully charged.
Storage mode, and float for that matter are generally for lead acid batteries.
“Storage mode”, for lithium batteries, consists of holding the charge level at 40% to 80%. Air transport limits it to 30%, but that is a bit on the low side since the specified self drain can send them below the dreaded 20% if they are in storage for >6 months. On the high side, >80%, the chemistry dislikes sitting there and it can cause up to 15% of capacity loss (permanently). For reference, just check out cell phone battery maintenance recommendations for maximum capacity/maximum life.
You are correct that a LFP should not be kept at full charge while in storage. This is not what “storage mode” in a charging algorithm means. It is a lower float charge meant to maintain the self discharge of a lead acid battery. Regarding a Multiplus, or any other Victron charger, it has nothing to do with storing a LFP battery.
I’m confused, obviously. I can’t understand why if you have a lithium battery mode wherein you put a maximum float charge 0.5V below the fully charged float level it won’t create the correct storage situation for lithium. Yes, it would be preferable to have that float voltage temperature-dependent, but over the range of temperatures that happen in my garage, it won’t be difficult to land within 20% of a recommended storage level. Ideally the system would put a small load on the battery in this condition to assure the battery makes it to that level, but it seems there is almost always a small load anyway (propane alarm for instance) which will meet that criteria.
I have an older RV that only has an Orion Tr-smart charger. For that I just add another battery type named “storage”. When I hook up to the AC supply in the garage, I just re-program the Orion to use the “storage” battery parameters. That is easy to do through Victron Connect on my iPhone.
But the newer RV with the MultiPlus-II needs a wired hook-up to use VE-Config on a Windows laptop to change battery types. Highly inconvenient.
Wayne, you can overcharge a Li battery with small currents over time (so the free lithium ions run out and exceeding so the correlating voltage).
So it is better to stop charging complete when the suitable criteria are met and reconnect later for recharging (no trickle charge!!)
Hi Karl-
For the Orion Tr-Smart, the charger won’t “sink” current. So if the battery is sitting at a higher voltage, this charger has no way to get the voltage down to the programmed “float” level. Hence this “reconnect” is an automatic process that happens only when the battery voltage falls below the programmed value (as is the “disconnect” when the “suitable criteria are met”–in this case, the float voltage).
The float condition is voltage driven, not current driven (although to maintain the float state there is a current limit in the charging direction).
Pb-acid doesn’t mind being held at full charge as long as the current is low enough to avoid significant self-heating, so there’s nothing wrong with just dumping an amp into the battery. I maintained “float” on a cruising sailboat by just hooking an 18W solar panel directly to it (100A-Hr, 12V, Group 27 battery). As you suggest, this would not be an acceptable solution for LiFePO4.
I see now that the manual for Victron Energy’s LiFePO4 batteries says the best storage is leave the batteries on “float” forever. My application uses these, so at least the warranty is still valid if you leave them at 100% charge.