Multi-Battery Charging - A Primer

At Clore Automotive, we get many questions each week related to multi-battery charging.

  • What is the best way to approach this task?
  • What are the benefits of the various approaches?
  • What is best for me and my particular situation?

There are really three approaches to multi-battery charging: series charging, parallel charging and multi-bank (multi-channel) charging. Below, we review the specifics of each approach.

Series Charging

In Series Charging, the batteries to be charged are connected in series, which combines the total voltage of all batteries and requires a charger that provides an equivalent output voltage. For instance, if you connect six 12V batteries in series, you would require a battery charger with 90V output voltage under load (to bring each battery to 14+ Volt finish charge).

The primary benefit of series charging is that, in such a configuration, all of the batteries in the series bank get the same charge current (while splitting the voltage between them). As a result, a bad battery in the bank (as long as it does not have an open cell) does not adversely affect the ability of the other batteries in the bank to get the charge they need. Because all batteries in the series bank get the total current of the charger, each of the good batteries gets charged as if there wasn’t a bad battery among them. This is very useful in unattended charging, such as overnight charging.

The drawback of series charging is that each bank to be charged requires the time and effort of establishing the series connection, wiring from battery 1 to battery 2, battery 2 to battery 3, etc. This process is somewhat cumbersome, and care must be taken to make sure the entire bank is wired properly prior to connecting a charger. Another limitation of this approach is the difficulty of scalability. The larger the battery bank, the higher output voltage required in the charger.

Parallel Charging

In Parallel Charging, the batteries to be charged are connected in parallel, which combines the total amperage (amp hours) of all batteries and requires a charger that provides an equivalent output current to bring the bank to full charge. For instance, if you connect 50 12V batteries in parallel, you would require a charger with 150-250 amps output current (which provides a nominal 3-5 amps per battery to be charged).

The primary benefit of parallel charging is the ease with which a large number of batteries can be connected, charged and disconnected. Parallel charging is done using bus bars, in which the charger is connected to a bus bar for the positive and negative outputs and the leads are dropped from the bus bars to each battery. As a result, the connection is quick and easy and charging can commence.

The main drawback of parallel charging is that a bad battery in the bank can affect the other batteries in the bank. For instance, if you were charging 50 batteries on 250A output charger and two of them were highly sulfated, the 250 amps of output current would not be evenly distributed among the 50 batteries. The two highly sulfated batteries would tend to monopolize the output current, absorbing as much as 80 amps each, leaving just 90 amps for the remaining 48 batteries. This likely would mean that the 48 good batteries will not reach full charge in the expected time, because their effective charge rate has been reduced.

Multi-Bank Charging

In Multi-Bank Charging, each battery is connected individually to the battery charger. As a result, this method does not combine either the voltage or the amperage of the batteries to be charged. Rather, each output lead is designed to charge a single battery and controls voltage and amperage accordingly. For instance, you could have a 4 bank charger for 12V batteries with a maximum output per lead of 15 amps.

The primary benefit of multi-bank charging is that each battery is individually charged independent of the other batteries connected to the charger. This means that the specific needs of that battery are being addressed. So, if one connected battery is bad, charging on that battery could be stopped without impacting the other charger outputs.

The main drawback to this method of charging, like series charging, is lack of scalability. If the requirement is to charge more batteries, additional chargers must be added. For instance, if you had a 10 output multi-bank battery charger but wanted to charge 50 batteries simultaneously, you would require 5 separate chargers.

Christie – The Answer to Multi-Battery Charging

The Christie brand of battery service products offers a wide variety of multi-battery charging solutions, from series to parallel to multi-bank charging. Christie battery chargers feature a wide variety of features that make charging safer, more efficient and more effective, including automatic reverse polarity protection, incorporated into many Christie battery chargers.

The Christie product offering includes three parallel chargers in our SA series, offering charging of up to 50 batteries simultaneously: SA10012 (20 batteries), SA17512 (35 batteries) and SA25012 (50 batteries). Made in the USA, they are designed to provide industrial duty continuous charging and feature and automatic taper as the battery bank reaches full charge.

Christie – Maximum Performance • Advanced Technology • Superior Quality