Di2 battery problem - now solved!

[pritchet74]

OK guys, something strange is going on with my Di2. As most of you know I have a highly customized Di2 kit on my bike - it has been operating flawlessly for the last 14 months, but last week I went to go for a ride and I couldn't get the shifters to work. I assumed it was the battery, so I charged it for 1 minute and plugged it back into the system and it was working perfectly. I had ridden the bike a couple of days before and everything was fine, so I assumed that the system sitting for a couple of days caused it to skip the "front derailleur will shut down and you will have about 100 miles with rear derailleur shifting before the system dies". I gave the system a full charge - as a reminder I am using the Di2 battery, but stripped out of the case and re-wired. So 1 week later puts me to today - I go for a ride and the system is dead again.

Does anyone have any thoughts? What's the life span for a Di2 battery?

[JudgeNick]

Sorry to hear that, Pritchet. I don't have any help to offer you, but I'm curious to see how this pans out. You've done some amazing work with Di2, and I hope to see your problem resolved soon.

[pritchet74]

So I got the battery hooked up to the charger this morning and it only charges for a couple minutes and then stops charging. I have to keep resetting the charger and re-doing it to get a couple minutes more charge. What the hell?!?

I think its time for a new battery / charger.

[coloclimber]

Whats new on the system? IIRC, It worked great when you had the stock shifters. Now, with the ergo's and buttons you are having problems. Maybe a short is draining the battery between the shifters junction where the adjuster is. ???

[pritchet74]

I thought about that, but the problem is now really that the battery doesn't seem to charge properly. It was dead yesterday and now it won't charge for more than 5 min at a time. After a 5 min charge I measured the voltage of the battery at 7.25V and now after several charges of 1-3 minutes its at 7.6V. Total charge time from the battery being dead is less than 30 min though and it takes 60-90 min to charge the battery full, right?

[dunlinii]

sounds like a duff battery to me?

[pritchet74]

Ya, I think so too. Luckily I have been pointed to a replacement battery and charger. $10 for the battery and $30 for the charger. Way cheaper than the Shimano parts. I just have to place the order.

[Gumgardner]

Go back to regular shifting. It's the way it should be.

[Juanmoretime]

Go back to regular shifting. It's the way it should be.

Yep, would not have been very nice if it would have happened in a race or while on a cycling trip........

[Gumgardner]

I can see all sorts of computer type glitches starting to creep up with this group. It's a year or so out. We'll see. I hope I'm wrong but...

[coloclimber]

Jeff's is anything but a Shimano Di2 group. It sounds like the replacement battery is cheaper than new cables and an easy fix. Report back how it works and fits.

[Ypsylon]

I can see all sorts of computer type glitches starting to creep up with this group. It's a year or so out. We'll see. I hope I'm wrong but...

In this case it is like using some yarn instead of steel cables and if that rips saying that mechanical shifting doesn't work.

[Jeffr]

First of all, if there was a short in the shifter buttons I would expect errant shifting behavior. There is a third button that is intended for flight deck and if that wire is shorted it could cause a low constant draw. There are certainly resistors in series and it would just be a trickle. Was battery life normal before you had this problem?

I would be somewhat concerned about identifying the source of the problem before just replacing the battery. Although at $10-$20 a piece I guess you can afford to experiment. The battery itself should not be particularly expensive. The shimano battery is only 800mAh

I am not an expert on battery chemistry but I have programmed charging circuits before. These batteries are probably two cells that should achieve roughly 4v each or 8v total at maximum capacity or 3.75 'nominally'. There are several stages to charging a lithium battery. In the first stage, the charger supplies constant current as the voltage rises. When the voltage reaches the peak there is then a slowly decreasing current saturation charge at constant voltage. If the current fails to rise in the first stage the charge will be aborted. This is likely your problem.

I believe it indicates chemical or physical damage to the cell which reduces the chemical storage capacity. This could've been caused by one really bad short which drained the cell too quickly if the overcurrent protection circuit was somehow insufficient. You might double-check the rest of the wiring in your seat-tube. It would have to come from somewhere in there, not beyond the front wiring harness. I would also see if the battery is abnormally hot when charging as this would also terminate the charge cycle. Is there a chance that it got wet?

As far as a source of batteries goes, sparkfun has some polymer lion batteries that weigh only 3g and store more energy than the shimano ones. You'd need two and a special charger that can handle two. They are only $7 each.

http://www.sparkfun.com/products/731

[Jeffr]

I can see all sorts of computer type glitches starting to creep up with this group. It's a year or so out. We'll see. I hope I'm wrong but...

The computational complexity involved in the stock shimano system is almost non-existent. The most complex part is the servo controller and these are so widely used and well understood, not to mention trivially simple, that I would not expect software bugs, etc. It is just a position aware motor.

In my opinion the most likely points of failure are not software but moisture and battery related. If you compare this to worn cables, failing springs and indexing wheels I would expect the MTBF to be similar if not biased for electronic. At least as the battery wears and runs out you get a predictable failure mode.

[pritchet74]

Thanks Jeff!

There's no moisture in the seatpost or seat tube. There is a chance that I screwed up the battery though - a month or 2 back I re-did some of my original wiring and (stupid me) I didn't disconnect the battery while I was doing it. A few times I had wires touching that shouldn't have been touching. I really think the problem is with the battery though and not any wiring as the function of the system is fine - the battery just won't charge properly.