Eunorau 52V 21Ah FLASH Secondary Battery Review

Described on the page as a HYFX-D LG3500 lithium battery, the 52V 21Ah pack is the secondary battery in Eunorau's FLASH range and is listed at $699. The page gives a weight of 13.9 lbs, a down tube battery type, a 4A standard charge and a cycle life of 500-800 times, and names the Eunorau Flash as the application bike.

Specifications

Options and pricing

A single variant at $699 is offered, in stock when read, with no crossed-out price and black as the color named. The table lists a 4A charger but the page does not say whether it is included in that price.

How it compares

At $699 this costs more than the other two FLASH packs: the Eunorau 52V 16Ah Main Battery for FLASH E-Bikes and the Eunorau 52V 17Ah Third Battery for FLASH E-Bikes are both $599. The Eunorau S500 and S1000 Second Battery (48V 27Ah) is $799 and is listed for the S500 and S1000 instead.

Shipping, returns and warranty

Shipping: the shipping page says accessories and batteries go by FedEx or UPS in an estimated 5 to 9 days after 1 to 3 business days of processing; orders over $100 ship free and smaller orders pay $14.99, with a possible remote-area charge. If the local warehouse is out of stock, the item ships from an overseas warehouse in an estimated 10 to 15 business days, and there may be no carrier tracking until it reaches the destination country and clears customs. The FAQ gives 15 to 20 days for batteries sent from China. Returns: an order can be cancelled for a full refund before it ships or is produced, but not after it ships; the page asks buyers not to refuse a delivered e-bike and to contact the store instead. A return must be applied for within 7 calendar days of receipt, the product must be new and re-sellable (not assembled, ridden, used or damaged) and complete with its manuals, accessories and original packaging, and the buyer ships it back within 7 days at their own cost to Eunorau's warehouses in the US, Australia, Europe or the UK. The store inspects it within 5 days and refunds in full when the fault is Eunorau's (wrong, damaged or defective item) or minus the shipping cost when the reason is the customer's. The terms page says customers are charged shipping only once, returns included, with no restocking fee, which does not match the return page's wording. Warranty: the warranty page lists 24 months for the battery, covering manufacturing defects only; it is void if the battery's seals are broken, if the wrong or a misused charger was used, or if the battery was used in equipment other than the bike it is specified for. It is for the original purchaser, excludes shipping damage (report it at once with photos or video) and does not cover labor. Disputes under the warranty go to binding individual arbitration (AAA rules, Nevada law) unless the buyer emails an opt-out within 30 days of purchase.

Before you buy

The page shows no customer reviews. Reputation: Eunorau E-Mobility USA Corp has an F grade on the Better Business Bureau, is not BBB accredited and has 2 complaints on file, both marked unanswered: a December 2025 request for proof that a bike sold as new was new, and a May 2025 report of a battery cover that would not latch, which the buyer attributes to a frame defect. A web search on 21 October 2026 found no Trustpilot page for Eunorau. The store says it has specialised in e-bikes since 2009 and designs its bikes in the US and manufactures them in Shanghai, while the BBB lists a business start date of 12 December 2019; the eunorau-ebike.com domain was registered on 27 July 2016.