Battery repair
 

I have a 3 yr old 48v 17 ah down tube battery I got with a Bafang bbshd kit with a problem w the on/off switch. A half a year ago the rocker on/off switch was inconsistent turning on so I left it on all the time then it started cutting out when hitting slight bumps. I’m usimg a cheap spare battery I got from Amazon. Curious if other folks have had similar problems. I ride off road most of the time and assumed the battery can take the vibration. I’m hoping this might be something I can fix myself once I have enough understanding of the problem. I figure shipping and repair costs would get me 25%+ to a new battery so gathering info now. While I ride off road I’m 67 and not going off jumps, 10-15 mph is my speed.

At 3yr old, you're starting to approach the lifetime of the battery. Li-ion chemistry starts to degrade at around 3yr and generally progresses more quickly as time goes on. Might not be worth fixing.

You'd have to take it apart to see how it was built . Often those packs are not soldered but spot welded almost so fixing them can be difficult. I doubt you're going to get anyone to fix it because no one would want the liability of the battery pack not knowing what it's been through (fire danger etc...) or the quality of it's safety circuits. It's kind of a lawsuit waiting to happen.

Depends on the battery and your skills. Some switches can be replaced with the same switch or a better one.

Might be OK to simply bypass the switch and leave the battery permanently turned on, like you already do. I only turn off my batteries that have LED lights glowing blue or red. Otherwise, I leave them turned on too.

Battery life depends on the battery too. I have a Haibike hardtail MTB with a Yamaha system that's six years old. The display reads the battery's state of charge (SOC) in percent. I've maintained the battery at 30% - 70% SOC and AFAICT it's still working great. The other day I rode about 10 miles of varied off road terrain in ECO mode (I seldom use any higher setting) and the battery used about 80 watt hours or 20% of its capacity. This suggests the battery is still capable of 40 miles or so.

Most battery cases are pretty easy to take apart. If it's cutting in/out while you're riding, my bet is on a loose wire somewhere. Shouldn't be difficult to diagnose and repair. I have many electrical devices that use batteries, and 3 years is not enough time to get rid of a battery. Sure it will lose some capacity, but there's still years left.

For my Ecotric 36 volt electric bike, this battery went right into the bike without any issues. I did need to use the included slide lock bar, because the hole for the battery lock was in a slightly different position.

Easy 1 screw change out. Battery came out of the box with more than half a charge so I was able to test it out immediately.

I've had issues with my charging jack on a RAD City bike. I had to remove the case and the charging plug interface was easy to work on. I did this work outside on a large patio. If you get one of these batteries burning by accidentally shorting it out you want lots of room outside around it so it won't burn down your workshop/home. The charging jack on mine needed some tightening however I could have done solder work where it was located with no problem. The battery cells were in a large welded tab assembly below the charging jack assembly and I didn't have trouble keeping away from them while repairing the jack. This simple cheap repair kept an expensive battery pack on the road where it is still working to this day.

There are two factors with the battery vibration:

1. Vibration of the battery itself, relating to its internal components
2. Vibration of the battery against the mount on the bike.

Either one of those things can shake something loose, loosen up connections, break solder joints, etc.
The battery mounting arrangement is something that deserves a lot of engineering effort, even on a road bike. (some roads will be even more jarring than offroad situations; with busted concrete...)