Hello. I have done around 8600 miles and counting on a total of 11 BB brand sla batteries. I am pedal assisting though lightly. Here's what I have learned:

1. No 2 batteries remain the same capacity throughout their life.
2. Some sla batteries loose cells for no reason. (warranty issues)
3. Be ready to parallel smaller sla's to your main sla's to extend life if one gets weak.
4. Have a voltmeter on each battery to find the weak one.

My stats:

BB BP 12ah - 5400 miles - one battery was replaced at 3000 miles.
BB Hr 9ah - 3200 miles and counting ( 2 weak batts being paralled with 5ah's, one replaced on warranty.

Chargers used - Soneil