I always like to recommend EM3EV, since Paul has a very good reputation at Endless-Sphere and is known for his great customer service.
Check-out this video about how EM3EV designs and produces their batteries. The next time I need new batteries for my trikes, I have to order from Paul. That is a completely different level of battery design and build quality, compared to my current batteries.
(the camera man/moderator guy is pretty annoying, though)