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Do I need to balance two Wattcycle 12V batteries in serial?

two_wheeled

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Jun 26, 2024
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Phoenix
Newbie question. I have two new Wattcycle 12V 100AH batteries connected in series for a 24V system. They were purchased as a pair and both arrived with exactly 13.1 volts. I've read and searched about needing to balance the batteries, but everything I'm reading appears to refer to balancing individual battery cells that someone would assemble themselves, not assembled batteries like these that have an internal BMS.
1. Do I still need to balance these two manually?
2. Can I top-balance them using my charge controller? I really don't want to have to buy a separate charger if I don't have to. My charge controller has options for voltage adjustments up to 30V, if that helps.

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Connect them in parallel and charge them to full. Connect them up in series and charge them with the 24v charger/AIO/whatever.

They will drift apart over time because of the tiny different in internal impeadance. If you keep the SOC between 20% and 80% this becomes less important.,.. if you full charge them daily the drift will be faster. You can install a 10 amp balancer to keep them in sync or you can disconnect everything, put them in parallel and charge them with a 12v charger every 3 months or so.
 
I can speak to experience on this subject.

First off I suggest a Smart shunt with mid point monitoring. The Victron is the best. The 300amp version is cheaper and more than enough for two batteries.

Anyways I have 2 12v 100 amp batteries in series. The mid point connection is a copper bus bar. The shunt always shows there is zero deviation except under high loads. Then I found a bad connection on the neg terminal. It wasn't tight enough.

But, I like to waste money so I bought a victron battery balancer. Waste of money. It does not even turn on until voltage gets to 27.3 volts. So 99 percent of the time it does nothing.

Then I put a small
load on one battery to pull it down to see if the balancer would correct it. Because I'm bored and stupid.

It didn't start to correct until the Smart shunt said the imbalance was .40 percent . I know that little bit don't matter, but it concerning when the shunt says they out .30 percent balance and the balancer isn't doing anything.

Anyway. If the batteries are balanced at the start and the connection are all done very well, the batteries will stay in balance. If not you can balance it by putting a small load in one battery.

Get the shunt and monitor it.

I bought a Chinese balancer, but has not arrived.
 
Also if need more Bluetooth range, get victron battery monitor. It's basically a smart shunt with a display, but the Bluetooth is stronger.
 
If you do a web search for HC-01 balancer, you will find what @wpns was talking about

EDIT: I'm too slow....... They are also available through Amazon or eBay, etc if you don't trust the ali-sites....
 
Got it, thanks. I ordered an HC02 - 4 batteries with LED. Thanks!

For other new people searching for this topic:
  • HA01 - no display, 2 battery capacity
  • HA02 - no display, 4 battery capacity
  • HC01 - LED voltage display, 2 battery capacity
  • HC02 - LED voltage display, 4 battery capacity
  • The HA02 & HC02 can be used with 2, 3, or 4 batteries.
 

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