12v Parallel Connections
Parallel connections are by far the easiest to understand. When two batteries are connected in parallel, their reserve capacity (Ah rating) as well as maximum discharge current (A rating) are multiplied by the quantity of batteries.
Take the example of the SOK 12v 100ah battery. One single battery can output a maximum of 100 amps continuous and has a reserve capacity of 100 amp-hours. This means that it could run a 10 amp load for 10 hours, and if the current was increased to 20 amps, it would last for 5 hours. Keep in mind, that this is assuming you started with a full-charged battery and ran it until it was completely depleted.
When two of the 12v 100ah batteries are connected in parallel, their maximum output current is now 200 amps, and the reserve capacity is 200 amp-hours. Now, we can run the same 10 amp load for 20 hours…and if we doubled the current, it would last half as long.
Further reading: How to determine the actual run-time remaining in your battery [Coming Soon]
Balancing When Connecting for Higher Voltages - 24v & 48v
Shipping regulations require LiFePO4 batteries to be discharged to 30% charge remaining prior to shipping. When connecting in parallel, the packs can easily balance, or share any differences in charge levels. If packs are not at an equal charge level, then they will not share the work equally.
When connecting in series, it is very important to charge all 12v batteries to the same charge level prior to reconfiguring in a higher-voltage configuration. Packs connected in series cannot share energy between packs, so it is essential to give the packs a healthy initial charge in a 12v parallel configuration prior to configuring in a series configuration.