Di2 battery failure

[shibshabdi2]

Was out for a cycle and toward the end, the gears stopped working. No prewarning where it puts it to the smaller ring.
I plugged the charger in and gears change, so I thought the batteries were the Issue. I purchased 14430 batteries and got a friend to replace them. The old batteries were tested and showing full 3.7v. Concerns were creeping in.
Plugged new batteries up, charged fulled, disconnected and they last about 6 seconds and then stops working.
Any suggestions at what to look at next, possibly junction box?

 

[TerryDi2]

I'd double check all connections, just to make sure.
If there is a broken wire or dodgy plug it'll probably be somewhere between the shifters and the battery... but it's hard to tell... it could be anything.

 

[the_mikey]

If the batteries are 3.7v they aren't flat, ideally a charged Lithium Ion cell would be 4.2v ish, and a low Lithium Ion cell will be 3.4v , below that it's effectively dead. A lithium Iron Phosphate battery runs at a slightly lower voltage and is considered flat at 3.0volts. It seems more likely that something else isn't working or a connection isn't quite right.

 

[Ridgeway]

I had an issue last year when my "fully charged" battery would die after a week or so (battery was only 12 months old). Battery got swapped out under warranty and goes what, no change, then the junction box, still the same.... then finally the LBS stripped down the entire system and re-installed it, since then no issues so must have been a poor connection that was draining the battery or not allowing enough power to pass through it.

I did devise a work around as this fault occurred a couple of time when out on the road. In the end i simply disconnected the rear derailleur cable and then did a reset and this seemed to cure it and allow me to get home.

My guess is it could well be a connection, check front and rear derailleur to start with, then the junction box.

 

[derrick]

Had a rear derailleur that would drain the battery in a week,. i disconnected the rear derailleur the battery never drained. changed to new rear derailleur no probs

 

[SheilaH]

You have to be careful with limiter screws on Di2 mechs. If the mech can't reach the end of its range of movement (because of limiter) it will keep activating.

 

[IanSmithCSE]

Good morning,

If you charge the battery fully and it lasts for only 6 seconds with both the old and new batteries then they sound fine.

Many lithium ion batteries are "protected", if you draw too much current this protection can act like a resettable fuse.

Recharging the battery will reset the Protection Circuit, so I would

Charge the battery fully.​

Leave idle for a day.​

Recharge without having being used. If this takes a very short period of time then the battery is holding charge. If the charge take a long time then both sets of cells are bad, unlikely but possible.​

Connect to the bike and let "go flat" in the mentioned 6 seconds.​

Recharge. If this takes a very short period of time then the battery is fine and you have probably tripped the protection and need to look for a short circuit. If the charge take a long time then both sets of cells are bad, unlikely but possible, if you can discharge the battery from fully charged to flat in 6 seconds it is going to get noticeably hot.​

Bye

Ian