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Replacement Battery

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Add a bigger battery to increase range and ride time.


These batteries, also known as Reention Dorado batteries, fit into the downtube frame of your Biktrix eBike. Made with top-of-the-line Samsung and Panasonic cells, it doesn't get much better than this.

  • Juggernaut Classic
  • Juggernaut Ultra 1000 & 1000 Pro
  • Juggernaut Ultra FS
  • Stunner LT
  • Stunner X
  • Stunner Step-Thru
  • Stunner Step-Over
  • Swift Step-Over
  • Swift Step-Thru
  • Skycap


These replacement batteries are enclosed within the frame of:

  • Juggernaut Ultra Beast (48V 15Ah)
  • Juggernaut Ultra FS Pro
  • Juggernaut Duos (52V 17Ah)
  • Swift Lite (36V 10Ah)

Range Extender

These Range Extender replacement batteries are compatible with the following eBikes:

  • Juggernaut Ultra Eagle (52V 21Ah only fits the large frame Eagle)
  • Juggernaut Duos** (additional battery)


**The following are NOT compatible with the 21Ah downtube batteries (if you are unsure of the fit, please email us):

  • 18.5" Ultra Duo 2 Step-Over
  • Classic Duo Step-Over
  • Ultra Duo 3 Step-Over

Charger included in each battery purchase.

Customer Reviews

Based on 33 reviews
Mike Archuleta

My card was charged October 6 I didn’t receive my battery till October 26. I specifically told the representative I needed battery before the 22nd.If you are ordering from bitrex allow 3 weeks to receive your order.

charlie Mercado

Great battery 52v 16ah however I'm getting better range from my replacement battery then the main battery which is 52v 17ah on pedal assist 2 I am getting 33 miles on the replacement battery and only 22 miles on the main battery

richard davis
spare battery

arrived in 2 weeks, works perfectly

Michael Slavik
Existing Battery has 3 pin charging connector. Replacement has 1 pin.

The website did not give me an option to pick the charger connector for the replacement battery. Although the replacement battery came with a charger, my plan to use the bike for commuting means I have to carry the charger for what ever battery I am using. I can not keep charger at location A and B for commuting. Plus, if the charger dies, I have to purchase a new one to match the battery.

Rod Matthews
48 v 21 amp battery add

Just received my second battery, a 48 v x 21 amp addition to the 52 v 17.5 amp I bought with my bike last June. The purpose is to avoid range anxiety. I took out the bike on a 35° day to try it out. After 20 miles, the 48 v battery said it was done and I skedaddled home. But after I brought the battery inside to warm up, I still had 3 dots on the battery indicator, not the one. So, don';t really know the range yet. I can get 30 miles on the 52 v. So I am hoping to get at least 40 miles from a 21 amp battery. We will see. Once I have broken in the battery [taking it down to at least 40% then recharging for the first few times] and begin riding in warmer weather, we will see how this battery does. In the meantime, I am very happy having a spare. If I'd waited until later in 2020, I definitely would have bought a step-through duo. I want to never have to worry about range ever again. Now that we have our COVID vaccines, my wife and I are ready to go [Yes, she has a backup battery for her Evelo bike]. Yeah 2021!

Tony Muzzin
I love bitrix!

Best money I’ve ever spent on anything!

Mitchell Jackson

Still awaiting delivery....

Luke Sanna
Beyond my highest expectations!

Biktrix Rox! From soup to nuts, everything about this order has been great. The battery is awesome and really extends my reach. Keep up the great work.



Marc Dear
Great price, reliable delivery

Thanks for the great service in sending me my back up battery!