Balancing multiple batteries in a bank

Q

I have a battery bank of six identical and same aged 140Ah Exide duals installed in my boat and I am concerned that the batteries are not connected in a fully balanced way. The setting up of four batteries is set out in various websites, but while they allude to the point that six or eight batteries can be connected I’ve not been able to convince myself that my expansion of the balanced system is correct. Can you provide a drawing of six batteries connected in an appropriately balanced way?

DUNCAN KENT REPLIES: Even very large diameter cables linking batteries together in parallel will generate some resistance, which may cause the system to be unbalanced both when charging and discharging. The following examples explain the worst and best ways to wire up a 6-way battery bank to ensure all the batteries get equal treatment.

Fig 1 If you take the power feed just from one end of the bank the battery furthest from the distribution end will be discharged the least, causing an imbalance in the system and the early demise of those batteries closer to the feeder terminals.

Fig 2 Linking them the same way but taking off the positive and negative feeds from opposite ends will help enormously to keep them balanced, but it still isn’t the ideal set up.

Fig 3 The only way to install a fully balanced multiple battery bank is to take equal length cables from each positive and negative terminal to a single +ve and -ve heavy-duty bus bar or power post, from which all distribution and charger connections are made. This isn’t always practical, though, and increases cable costs considerably, so while the configuration in Fig 3 isn’t perfect, it’s probably as close as is practical with six batteries.