Out of exasperation I gave up on traditional ebike battery bags a couple of years ago since they were all constructed so poorly and would end up ripping after a couple of months. I wanted to share with the community what I have discovered to be a vastly superior solution to battery bags: wide mouth tool bags.
Here's a smaller one I use with a 52V 15Ah LiPo battery I built: http://a.co/hiKmc0S
I've also had good luck with the Black & Decker 14" wide mouth tool bag for my bigger batteries: http://a.co/fnLQgkX
So what makes them so great?
1. Extremely durable, designed to be abused, weatherproof
2. The wide mouth makes putting the battery (or batteries if you are a LiPo guy) in and taking them out very easy
3. The wide mouth lets you inspect the batteries and get access to all of the balancing ports and BMS
4. The sides are structured so it supports the batteries better than a normal battery bag and has some impact resistance
5. The mouth is structured and distributes any weight on top of it over the entire bag
6. There are the perfect amount of minimalist pockets for random bike parts or tools on the side or inside the bag (I would avoid metal tools INSIDE the bag
7. The zipper zips down low on the side so you can have your cables exiting the bag without exposing the battery to the weather
8. The zipper stays in position down low on the side and doesn't open on its own
9. You can zip the wires and connectors completely into the bag so it looks like a normal bag if you have to bring it into a store or at work
Tons of room (this is a 52V 15h LiPo battery but you could probably fit up to 25Ah into it):