You can use up to two of our Lithium 12v / 24v batteries in series and up to four in parallel packs. You should arrange your charge setup so that each battery in the pack is individually connected to a charger. Batteries should be of the same model, and purchased together at the same time, to ensure they have similar performance characteristics.
For example, a 24v pack made up of two 12v Lithium batteries connected in series should be charged by two 12v chargers (or a dual-output 12v charger), with a set of charge leads individually connected to each battery in the pack.
A single 24v charger connected to the 24v pack output is not recommended, for reasons outlined below. Similar advice applies if you wire two 12v Lithium batteries in parallel to provide double the capacity at 12v - a single 12v charger connected to the output wiring of a parallel pack is not ideal, due to the risk of individual battery voltage varying over time.
Why this matters: Lithium batteries of any brand can be irreversibly damaged if they are discharged too deeply past their rest voltage. To prevent this damage, the manufacturers equip the batteries with a built-in BMS (Battery Management System) that will monitor the voltage of the cells inside, and locks the battery into a protection mode that stops it from discharging if the cells inside are getting too low. Most chargers cannot automatically reset this protection mode in a single battery, and no chargers connected to a pack output can reset a single battery in a pack (This is because the protected batteries require a high initial voltage to switch them back on again, and if there are two or more batteries connected in a pack, the first one to start charging may stop the second one from getting reset, because it will immediately pull the charge voltage down).
Batteries put in a pack will end up with slightly different charge states over time when charged as a pack instead of individually, and this is accelerated if the wiring is not set up correctly.
Once the voltages of the individual batteries start to drift apart, this results in a risk that a deep discharge will cause the BMS to cut-off the discharge to protect one battery before the others reach the cut-off voltage. When this happens, a pack charger will not be able to recharge that cut-off battery in the pack automatically, leading to more imbalance and lower-than-expected output voltage or capacity. This can happen to any brand of Lithium battery charged in packs instead of individually. Supplying the batteries in the pack with individual chargers/individual charge leads, and not discharging them completely flat, will significantly reduce the risk of this issue occurring.
The vast majority of Lithium battery warranty enquiries our stores get are for batteries used in packs wired to a single charger where the batteries experienced BMS cut-off - they worked fine once their BMS was reset.
If you have a 12v Lithium battery in a pack that has been over-discharged and the BMS has entered the protection mode, follow these instructions to reset it.
If you are looking for a 24v Lithium solution, please have a look at our 24v SB2218.
Suitable chargers for SB2218 are MB3960 and MP3741
If you are looking for a high-capacity 12v Lithium solution, please have a look at our 200Ah SB2217.
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