German Lab Test Fails 3 of 5 Balcony Solar Batteries on Interference
By Priya Nair · Last reviewed Stiftung Warentest, Germany's consumer-testing institute, published laboratory results for balcony solar storage systems: three of five tested products emitted electromagnetic interference above permitted limits. Anker's Solarbank line took the only satisfactory grade; EcoFlow's Stream Ultra was rated poor (4.7). The findings moved several WattRank scores.
Germany's Stiftung Warentest — the country's independent consumer-testing institute, and the closest thing the balcony-solar category has to a referee — put five storage systems through its laboratory in 2026, and the results were uncomfortable for most of the market. Three of the five products emitted electromagnetic interference above permitted limits, the kind of emissions that can disturb routers, speakers and televisions in the surrounding home. Only two products stayed near the threshold, and only one — Anker's Solarbank — earned a satisfactory overall grade. EcoFlow's Stream Ultra received a 4.7, a poor rating, despite its strong consumer reviews and feature set.
The finding matters beyond Germany for two reasons. First, it is a rare instrument-grade look at build quality in a category where most published reviews are impressions: electromagnetic compliance is a proxy for engineering discipline in filtering, shielding and thermal design — precisely the places where cost-cutting is invisible in a product photo. Second, several of the tested systems ship across Europe and their platforms are arriving in other markets, so the results travel with them.
WattRank's scores reflect the test: the Anker Solarbank 4 Pro's position at the top of our worldwide ranking rests in part on its line's laboratory record, and the Stream Ultra carries an explicit penalty with the finding noted on its fact sheet. Our methodology weighs independent laboratory evidence above all other review input — results like these are exactly why.