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Would it be okay to charge four identical 12 V batteries in series-parallel, using a 24 V charger, as shown?

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I am trying to create a 24 V battery bank, so naturally I need to connect two 12 V batteries in series. I also need a larger capacity than these batteries can supply, so I intend to wire up two more 12 V batteries in parallel for a total of four. I have a 24 V charger for this battery bank, but will it be able to safely and effectively charge all four of the batteries wired in this configuration?

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    \$\begingroup\$ It appears that your diagram has the 24 volt charger completely shorted out. \$\endgroup\$
    – Andy aka
    Commented Jun 2, 2020 at 13:41
  • \$\begingroup\$ Not only is the charger shorted, but you need to make sure the current flow is corre3ct through each battery. \$\endgroup\$
    – Solar Mike
    Commented Jun 2, 2020 at 13:47
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    \$\begingroup\$ If you post a diagram like that, you should not do anything with components. Stick to ready made. \$\endgroup\$
    – Neil_UK
    Commented Jun 2, 2020 at 13:48
  • \$\begingroup\$ The comments above are valid but the larger question remains if a combination of batteries in series and parallel can be effectively charged \$\endgroup\$
    – Jack Conway
    Commented Jun 2, 2020 at 14:14
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    \$\begingroup\$ You can only really float charge parallel lead acid batteries. \$\endgroup\$
    – Andy aka
    Commented Jun 2, 2020 at 14:20

3 Answers 3

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Charging and discharging batteries in series can lead to voltage imbalance over time. You can read more about it here. To get the most lifetime from your batteries, you can charge them in series but then you should have a charge balancing circuit.

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    \$\begingroup\$ A 12 volt lead-acid battery consists of six, 2 volt cells connected in series, with no battery mangement/charge balancing circuits. Why wouldl you need charge balancing circuits when you connect two such batteries in series? \$\endgroup\$
    – Peter Bennett
    Commented Jul 22, 2020 at 1:01
  • \$\begingroup\$ @PeterBennett Good question. This is necessary to prolong the lifetime of batteries that are series connected. It applies to all battery chemistries, not just lead acid. If you don't do it, one battery may end up becoming overcharged over time and another undercharged. You can read more about it here: eenewsautomotive.com/content/balancing-lead-acid-batteries \$\endgroup\$
    – mr_js
    Commented Jul 22, 2020 at 10:46
  • \$\begingroup\$ @mr_js, while technically you are correct, in practice this is not an issue with only two lead-acid batteries in series. Towards the end of charge, the most charged L.A. battery just generates some hydrogen, while the other one finishes charging. At the end, the two L.A. batteries are balanced. Indeed, this effect is happening at the cell level, whether just a 12 V battery, or two 12 V batteries in series. \$\endgroup\$
    – Davide Andrea
    Commented Oct 5, 2021 at 21:19
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I assume they are lead-acid batteries.

If so, yes, what you are doing will work. Indeed, this is exactly what the industry has been doing for a century.

Despite what others have said, imbalance is not a significant issue with only two 12 V lead acid batteries in series, because at the end of charge the most charged battery will handle a bit of overcharge as the other battery finishes charging.

(Conversely, if these are Li-ion batteries, a whole lot of issues would arise, especially depending on whether or not they are protected batteries.)

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voltage is doubled when connected in series, but amperage stays the same. When connected in parallel, amperage doubles but voltage stays the same. Wire 2 batteries parallel and then wire the other 2 the same. Then wire one set to the other set in series. Problem solved.

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  • \$\begingroup\$ This does not answer OPs question. \$\endgroup\$
    – winny
    Commented Jul 21, 2020 at 8:37
  • \$\begingroup\$ We don't normally say "amperage" around these parts. We prefer "current". \$\endgroup\$
    – Davide Andrea
    Commented Oct 5, 2021 at 21:13

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