• Description

BI 1203-S Isolator

Onboard systems usually consist of two or more batteries that function independently when powering the 12 or 24V consumers. These batteries require independent charging with reliable battery isolators or battery combiners.

Mastervolt offers several intelligent solutions:

  • Battery isolators that divide your charge current with a minimum energy loss.
  • The Charge Mate for connecting and/or disconnecting two batteries.
  • Battery Watch for monitoring the condition of your batteries (also usable as the main switch).

Battery isolators for conventional systems with an alternator or battery charger and two or three batteries

Mastervolt’s BI battery isolators are based on conventional diode technology. The diode voltage drop (ca. 0.6 V) can be compensated for by adapting the output voltage of the connected charger or alternator. Mastervolt Mass battery chargers and Alpha Pro charge regulators are standardly equipped with automatic voltage drop compensation.

Compact and lightweight

The Mastervolt BI battery isolators are compact and fully solid-state, preventing wear. The weight varies from 580 to 1300 grams.

Robust and durable

Completely corrosion-proof material with aluminum heat sinks. The electronic components are encased in synthetic materials, the BI models have molded diode splitters.

Fast installation

The synthetic end plates feature connection lugs, the solid bolt connections with nuts and locking rings ensure easy installation.


Owner's Manual (pdf)
Brochure (pdf)

Frequently Asked Questions

Yes! We provide free and fast shipping on MOST orders within the continental United States. However, some specific brands and items will require a quote. You can live chat or call us for a quote
Most orders ship out within 1–2 business days and arrive within 3–5 business days depending on your location.
We offer easy returns as long as your item meets the conditions outlined in our Return Policy. Items must be unused, in original packaging, and returned within the specified return window.
Absolutely! Our in-house product experts are here to help. Live chat or call us 513-743-829 for personalized advice before or after your purchase.
Yes. All products include any applicable manufacturer warranties, and we’ll help you handle any warranty claims if needed.
Yes, we only sell 100% authentic, brand-new products, sourced directly from our manufacturers or authorized distributors.
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Feedback From Our Customers

At Green Vista Living, we pride ourselves on delivering top-quality products and exceptional service to solar professionals and homeowners alike. Here's what our customers have to say about their experiences with us.

Kevin Leary
May 18, 2025
★★★★★

Incredible Tech Support from Anees of Green Vista Living. Exceptional service and went above and beyond on every question.

Bryan Cunningham
Off grid Kit • Dec 21, 2025
★★★★★

Shipment was slow due to high demand, but the team kept me informed and ensured everything arrived properly.

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