Di2 Battery Life





To get a feel for Di2 battery life, I’m tracking the number of days as well as the number of hours the trike was moving (and therefor shifting and with the display on) between each charge.  The chart at the top shows the distance and number of days between charges since I settled on a consistent configuration:  Ultegra derailleur and Alfine display programmed to turn off after 5 seconds.  A discharge cycle for this graph is from full charge (4 bars) to 1 bar.  I figure in practice I’ll recharge as soon as I hit one bar so that I have an entire bar of “fudge”.  So the time between charges shown in the graph should be easily attainable, repeatedly.

The charts show the run down for the first four discharge cycles of the battery’s life, spanning all four seasons in the Boise high desert.  For the first two I ran it all the way to zero bars and dead battery just to explore the limit, and to get a feel for how much fudge that last bar provides. The third cycle represents how I plan to manage charging here on out:  when it hits 1 bar, charge it when I get a chance, knowing I should have at least a couple weeks grace period. I’ve also plotted each day’s maximum and minimum outside air temperature in an effort to determine how much temperature affects battery life.  The trike is stored in an unconditioned garage and parked outside at work.

I’m no longer concerned about battery life, though the first discharge cycle had me worried.  35 days between charges is pretty good, but only 17 hours of total ride time in that period is really low.  On a tour I could use this up in a few days.  Thankfully the combination of warmer temperatures, Ultegra derailleur instead of Alfine motor, and 5 instead of 300 seconds display time have all contributed to a substantial increase in battery life.  3 months, 700 miles, and 64 hours moving during prime touring season is fantastic.  Granted these were all commuting / recreational miles, so maybe a month on the road before even having to think about charging.  I can live with that.

9 thoughts on “Di2 Battery Life

  1. mkzig

    This looks great to me. Just the information I would want to see. It looks like the battery won’t go months before recharge, but a week to 10 days seems excellent to me.


  2. Kurt Post author

    It seems OK until you look at the number of hours the system has been “on”, or moving. I’m at half battery with only 4.5 hours of actual use. Probably fine for commuting or weekend trips but if you figure 5 hours of riding per day for a cross-country trip I wouldn’t even get two days at the current discharge rate. This assumes that discharge in the non-moving state is negligible compared with discharge while moving (and therefor shifting and running the display) which so far seems to be the case.

    My minimum threshold for time between charges on a tour is probably about a week. I’m not sure Di2 is going to get me there. Some things that will hopefully help: warmer temperatures and running the non-display cockpit controller. And charge capacity might improve after a cycle or two. At some point I’ll measure the difference in current draw between the non-display controller and the Alfine display with the display on. The only obvious difference between the two is powering the display itself, shifting should be the same with either controller. We’ll see…


      1. Kurt Post author

        Either something in the system is drawing too much current, your charger is dead, or your battery is dead. Without knowing any more details of your situation, I’d say it’s most likely your battery. My brother has an identical setup as mine and it eventually became apparent that his battery was defective from the factory, though his lasted much longer than 12 hours. He recently replaced it, we’re waiting to see if that solves his problem. Shimano wasn’t much help BTW, he ended up buying a new battery to avoid the down time of waiting for Shimano to evaluate the defective battery and (maybe) replace it. We’ll see if they replace it when he sends it in now. One thing Shimano did say is that they had a run of defective batteries at one point that made it into customers’ hands– depending on the age of your battery it could be one of these.

        Some easy things to try:
        1) Start a new charging cycle and make sure the charge light stays on and doesn’t show any error conditions for more than a few minutes. I can’t remember offhand what the light(s) on the charger mean but if it’s not obvious, the manual should say. A failure here indicates a bad battery or charger.
        2) After a full charge, remove the charger and run the derailleur through its gears on the bench. Make sure everything is operating normally– you can reach each gear cleanly and move the chain without any unusual noise or binding. With everything at rest, listen closely to the motor in the derailleur (or on the hub if Alfine) for any noise that would indicate it is operating (and hence drawing current) when it should be effectively turned off.
        3) Hook the system up to a computer running the Shimano E-Tube software and make sure all the components show up normally and have the latest firmware.

        A bit harder:
        4) If you’re handy with a DVM, measure the current between the battery and the first E-Tube junction while the bike is at rest, at full charge, and charger disconnected. You can read about how I did this here: https://seasonalcommute.com/2015/02/16/di2-battery-life/. I’d expect to see about .015 ma (15 micro-amps) using either an Ultegra cockpit junction box or Alfine display with the display turned off. Much more than that indicates a problem in one of the components downstream of the battery, most likely the motor/derailleur or junction box/display unit.

        If you know a decent bike shop that can spell Di2, they should be able to do all of this for you and make it right with Shimano. Good luck and let us know how it goes!


  3. Kurt Post author

    BTW most sites selling the SM-BTR2 battery I’m testing quote the following. I don’t know what the source of this text is but it doesn’t appear to be Shimano.

    “The Di2 battery lasts from between 600 to 1,500 miles between charges. You can expect that lots of shifting in cold, cold weather will result in shorter battery life, but we’ve found that 1,000 miles is an average interval. There is no “charge memory” in the battery, so you can recharge it as often as you like, though Shimano recommends once a week or so if you’re a daily rider. The battery can go 300 charge cycles at 100% integrity; charging once a week means almost six years.”

    If you figure the average interval quoted is based on racers averaging, say, 20 MPH and a typical self-supported touring pace is more like 10 MPH, then I’d expect about half the quoted mileage average, so 500 miles between charges. This would be more than enough, but I’m currently on track for not much more than 100 miles between charges, and (I hope) I average more than 10 MPH on my commute. I think it’s safe to assume this quote is based on warm riding temps and not the Alfine controller with the display. So maybe this explains the difference. Or maybe I’m not accurately accounting for the difference in my riding vs. the riding used for the quoted average. Or maybe that quote is BS. Time will tell…


  4. Kurt Post author

    It’s articles like this one (http://blog.tri-sports.com/2011/04/25/shimano-di2-battery-life-after-death) that led me to be pretty unconcerned about Di2 battery life. Over nine months (July – April) and 3200 miles on a single charge, seems unbelievable. I think this was Dura-Ace Di2 with external derailleurs and the BTR-1 battery instead of my BTR-2 battery. But Shimano claims Di2 with the BTR-2 battery has longer range (1200 vs 1000 miles). And if anything I’d think the energy required to shift an IGH is significantly less than derailleurs, though I’ve never seen any numbers on that. Another possible source of the difference is that my battery gauge is _very_ nonlinear. Or maybe I just have a bad battery. Will keep plotting and see where the numbers fall.


  5. Pingback: Life After Alfine | A Seasonal Commute

  6. Pingback: Di2 Battery Life | A Seasonal Commute

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