Certain batteries have limitations as to whether they can be connected in parallel or series. This post aims to clarify this topic.
Models of batteries:
- Base – This battery is the original design SOK battery that has no Bluetooth or heating pads.
- Plus – This is the newer version that has Bluetooth functionality, but no heating pads.
- Pro – Features both Bluetooth and heating pads. This is also known as the “H” model.
12 Volt Batteries:
- 100ah & 206ah Base & Plus: 4 in series, unlimited parallel, battery balancer highly recommended for 36/48v systems
- 100ah & 206ah Pro: No series connections allowed
24 Volt Batteries:
- 100ah Base & plus: 2 in series, unlimited parallel. Battery balancer optional
48 Volt Pro Batteries (Equipped with LCD screen):
- No series connections allowed. Communication supported up to 15 in parallel, unlimited parallel without communication.
48 Volt Base Batteries (No LCD screen):
- No series connections allowed. Unlimited parallel connections.
Why are external Battery Balancers recommended?
The BMS within the battery only is intended to monitor and balance the cells within the battery enclosure it is mounted in, thus, when batteries are in series one battery has no idea what is going on with the rest of the chain. This also means that it cannot match itself to the other batteries in the chain because it is unable to monitor the charge levels of the other batteries.
For batteries to work in series, all batteries in the chain must be at the same charge level. In order to run without an external balancer, then you must fully charge the batteries to 100% with a 12 volt charger BEFORE connecting them in series. Systems without balancers should be checked manually monthly for drift in charge level. This is accomplished by fully charging the system and comparing the voltage of the two packs. If they are more then .3v different, then it would be required to top off each battery individually. If however, you do add the external balancer, then the balancer is able to monitor and correct for differences in terms of SOC% across the battery string.
Normally, a 2-series system won’t have much deviation, so fully charging each battery before commissioning the system should be sufficient, however, on a 3- or 4-series system, there are multiple batteries that have a much greater chance of deviating, necessitating the need for the external balancing system.
What Battery Balancers are recommended?
Multiple options are available, listed from highest recommendation to lowest:
- Victron Battery Balancer (24/36/48v systems)- available here: https://www.currentconnected.com/product/ve-batbal/
- ISunEnergy Battery Balancer – (24/36/48v systems) available here: https://www.amazon.com/iSunergy-Equalizer-Balan…
- Universal 48v Battery Balancer – (48v systems) available here: https://watts247.com/product/eq-48-4-48v-universal-…