New 52v battery with existing 48V battery

[reggy]

Hi,
I'm looking for a second 52v battery. Have an existing 48v-14aH battery on my radmini4, and looking best way to either run them in parallel or separately. Any idea why a similar battery is prices differently from each company? Do you get what you pay for with batteries? The Electro Bike battery are $170 dollars more expensive, is it worth it?

Electro Bike World 52v 17Ah Fat Shark Battery $739.99 "uses AODA cells"
https://a3ee3610-0553-11e5-8794-f04da2069d31.onlinestore.godaddy.com/products/52v-17-5ah-fat-shark-battery

EUNORAU 52V17AH Down Tube Ebike Battery For Conversion Kit $569.00 USD "All the battery from EUNORAU with original SANYO,LG,SAMSUNG cells"
https://eunorau-ebike.com/products/eunorau-52v17ah-b05-hailong-ebike-battery?_pos=4&_sid=4c318e8f2&_ss=r

Anyone using a EUNORAU Dual Battery Hardware Converter or similar like the datex2?
https://eunorau-ebike.com/products/eunorau-ebike-24v-36v-48v-52v-dual-battery-hardware-converter-dual-battery-parallel-connector?_pos=1&_sid=77ba0505b&_ss=r
I've emailed Electro Bike World, and they said they don't recommend using this device as it degrades the batteries quicker. Recommends using one battery at a time instead. Can anyone comment? Of have experience with either of the batteries listed?

Cheers,
Martin