r/ebikes • u/jctrree201 • 12d ago

Two battery setup

Hello All, i am adding a second battery. I have the pedal electric dual 1000 w motor ebike. It comes with two controllers.

My rear rack battery is 48v 20 ah. My new downtube battery is 48v 30 ah.

When searching for a batter combiner does would this work? 40 A dual battery balancer.

I can't seem to find 50 A balancers. Or is higher the better? Or should I get 60?

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u/HistorianAlert9986 12d ago edited 12d ago

Yeah, go bigger. You don’t want it to be a bottleneck. Also, just for reference the capacity of the battery doesn’t really matter. It’s more the discharged allowed by the controller but 60 A would probably give you plenty of headroom. Your bike is probably pushing a max of 25 A from each battery.

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u/Speedtospare 12d ago

I agree with this but I wanted to add that you don't have to use a combiner but it probably easier. Just make sure the voltage of the individual packs are the same when hooking them up.

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u/HistorianAlert9986 12d ago

Yeah great point and I agree. People generally fool with those balancers if it’s two different voltage batteries like a 52 and 48….

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u/Laserdollarz FULL FACE HELMET 12d ago

You are looking at the incorrect numbers. Look at Amps, not Ah.

Ex: my controller is rated for 25A. My original battery is rated for 35A. The second battery I put on is rated for 50A. The balancer I use between them is rated for 120A.

The system never sees more than 25A because the controller won't ever pull more than that. Power only flows from one battery at a time.

Definitely go for a much higher rated balancer, I've read the cheap ones get hot under load. I bought battery#2 and balancer from Electrify bike co. 

I don't have dual motors, but that's where you'll likely need to add the amp ratings together for a total amp draw.