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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?

Null
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Jack Conway
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    It appears that your diagram has the 24 volt charger completely shorted out. – Andy aka Jun 02 '20 at 13:41
  • Not only is the charger shorted, but you need to make sure the current flow is corre3ct through each battery. – Solar Mike Jun 02 '20 at 13:47
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    If you post a diagram like that, you should not do anything with components. Stick to ready made. – Neil_UK Jun 02 '20 at 13:48
  • The comments above are valid but the larger question remains if a combination of batteries in series and parallel can be effectively charged – Jack Conway Jun 02 '20 at 14:14
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    You can only really float charge parallel lead acid batteries. – Andy aka Jun 02 '20 at 14:20
  • Golf carts do this. Many work with multiple 12V batteries to drive a 48V motor. Check out: https://petesgolfcarts.com/battery-charger-knowledge/ For a few schematics. And I third the above suggestion - Don't actually try building one - Just buy a commercially complete setup. No offense brother, but you will hurt yourself. You don't wanna be at the receiving end of a pi$$ed off lead-acid battery. – Kyle B Jun 02 '20 at 15:41
  • You diagram is dangerously incorrect, but you already know that. It is OK to parallel/series charge 12V batteries. It's the only way to create 24, 36 or 48V systems with higher capacity (for example in marine power systems). This will work as long as all of the batteries are of the same technology (i.e. GEL, AGM, or regular Lead Acid), have the same capacity and preferably the same age. – StarCat Jun 02 '20 at 15:44
  • @Andy Aka. I don't agree. As long as all of the batteries have the same charge characteristics, you can treat them as one single large battery bank and charge them accordingly. Look at power systems for yachts or off-grid use. There are battery balancers available that can prevent individual batteries in a bank from becoming over- or undercharged. – StarCat Jun 02 '20 at 16:01
  • @StarCat - https://electronics.stackexchange.com/questions/22995/floating-multiple-sealed-lead-acid-batteries-in-parallel#:~:text=In%20theory%20it%20is%20OK,they%20are%20very%20run%20down. – Andy aka Jun 02 '20 at 16:01
  • @Andy aka, https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf and remember that every 12V lead acid battery is in itself a bank of 6 x 2V batteries in series. – StarCat Jun 02 '20 at 16:03
  • Realistically, large lead acid battery banks incorporate series and parallel connections all the time. I think there is an assumption that they will be reasonably well managed so that trickle charging is not required. Also sudden changes in capacity which could indicate a failed battery, should be investigated immediately. – user57037 Jun 02 '20 at 22:32
  • The error in the schematic has been rectified. – vu2nan Aug 21 '20 at 04:43

3 Answers3

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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.

mr_js
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    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? – Peter Bennett Jul 22 '20 at 01:01
  • @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: https://www.eenewsautomotive.com/content/balancing-lead-acid-batteries – mr_js Jul 22 '20 at 10:46
  • @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. – Davide Andrea Oct 05 '21 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.)

Davide Andrea
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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.

AJN
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user258115
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