Tandem battery indicator problem

The following happened to me today, and once before a few weeks ago. I checked my Tandem t:slim X2’s battery, and it was reading at (I think) 35 or 40%. I decided to take advantage of a computer session, and plugged it in. Some time later (I wish I had noted down the time), I checked it again, and it was down to 5%! While being charged!

I let it keep charging, and it built back up to 45% at the usual rate. I went out for a walk, and came back and plugged it in. In about five minutes, it was showing 100%!

The first time a similar event took place, I emailed Tandem Customer Service. A tech got back to me fairly quickly. She told me this was not unusual, and mentioned that some users make it a practice to charge the pump for a few minutes every day, just to make sure it’s OK.

This seems wrong to me. We should use a workaround to make up for defective technology?! And we can’t trust the battery level number displayed?! That’s something that seems like it should be fixed! I’m going to try to record this so I have some data to submit.

Now: normally I get several days, over a week, on a charge. So it’s not like the battery is failing. It’s just the level display seems to get stuck at too high a reading for a while, until you plug in the charger, whereupon it drops down to the correct–low!–level. Or maybe it’s the LOW reading that is incorrect! How would I know?!

Anyone else have a similar experience?


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I’ve learned 2 things with tech support (not just Tandem, all of them).

  1. If you don’t like the response you got, call back and speak to someone else. Techs with different experience, and even different training classes, can give you very different responses. If you’re lucky, you’ll get one who’s been around for a while. They’re quicker to notice what’s really atypical, and work a little harder to find a solution.

  2. They all have a rule book to follow. If you have a problem that isn’t clearly spelled out in their rule book, it helps to figure out what IS in the rule book and rephrase your comments to work within their guidelines.

The old techs are the absolute best. The ones who were trained up when Tandem was really small and all about the best possible customer service. It costs the company almost nothing to exchange a pump, but keeping customers happy and retaining their business at the end of their warranty period is priceless. The new techs haven’t all gotten that memo yet. Some of them seem to think they’re protecting their jobs by being miserly.

In this particular case, Tandem specifies that a pump shouldn’t lose more than 50% charge in 3 days. (I was told that before Control-IQ, though, it might be a different number now.) If it does, it’s our of spec and qualifies for a replacement. So next time it shows you 5%, or any other crazy drop, you can call it in and say it’s lost 95% of it’s charge in [?] days, rather than calling it a “glitch”. It may not even come to creative language with the right tech. I only know all this because a tech told me my pump was out of spec when I was calling about an unrelated sensor issue and they looked at my uploads. (I know it was actually my fault because I was notorious for ignoring the vibrating alerts, which kills the battery stupid fast. I go more than a week between charges without vibration.)

There’s also a backdoor loophole not many people know about. If you have a problem that tech support can’t help you with because it’s not in any of their guidance, they can set you up with an appointment with one of their diabetic educators. There’s no foul in telling them point blank that you know about this loophole and would like to proceed this way. The DE can request a new pump for you without having to follow the same rulebook the techs do. You basically just have to talk to them and explain that you know the right way to use the pump and you’re not doing anything silly, and the the pump really is behaving badly.


Mine did this over a year ago and they immediately sent me a new pump.

Another possibility for the battery level error. I had this happen about a year ago. Talking with the Tandem tech support, I found that if you use a charger that doesn’t have enough oomph in it to properly charge the pump, it can mess up the battery indicator. In my case, I was using an iPhone charger - not enough wattage for charging the pump. Now I use an old iGo charger or an iPad charger, both of which put out enough current to avoid problems.

I should mention that the low-wattage may still charge the pump to 100% over a longer time, but the battery indicator could be wrong. For me, it said 100% when I unplugged it, then a couple minutes later it said 5%.

None of this should happen if you’re using the actual Tandem-supplied charger.

My armchair now looks like the electric chair, in that I have chargers for iPhone, iPad, Surface Pro, And Dell laptop. I also keep a charged Jackery battery power supply handy when I go out. That will get a workout starting Nov. 2, when I go in the hospital for CRS/HIPEC surgery, followed by probably two weeks as an inpatient. That will be an adventure!

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Hi Keith–I’m getting frustrated also with the issues with the battery/charger. I have contacted Tandem 3 times with no resolution. The first time pump said 65% battery, plugged it in & pump said it was 20%. Waited until it was back up to 85% & called Tandem to clarify, but the response was similar to yours–“it happens”. Second time battery level was at 75%, plugged it in & it went to 5%–left it charged for almost an hour & it never even got up to 50%. Tandem rep said it was probably something I was doing, but couldn’t tell that could be. Third time I went to bed with 85% charge, woke up to 5%. Plugged it in & it said 95%–go figure! When I called Tandem, the rep said she would have her supervisor call me as she didn’t know, but I never heard back from anyone. I was told by my Tandem trainer to plug it in before you shower to make sure you always have enough charge, but now I feel I can’t trust what it says. I love the information posted by others regarding this issue & I will definitely take advantage of it next time I call.

You can reset the battery indicator by powering off and then powering back on.
However you will lose the current cartridge settings.
So you will need to go through a new cartridge load.
I tried this and my battery indicator started working normally again.

I always charge it completely and always with a direct car or wall charger. Keep a usb charger for emergencies or when I forgot to charge it.

This has happened to me twice in 3-1/2 years. I haven’t upgraded the pump software to either Basal or Control IQ. I charge it for a long time but it says 5%. Then it alarms about low charge. Tandem tech had me shut the pump off, then turn it back on, then plug it in for awhile more, half hour? Then check, and it said 100%, seemed to solve it. The second time, a couple days ago, I just plugged it back in for awhile and it sorted itself out.

I agree, it’s a serious concern, and they ought to fix it, and/or give us a new pump.

We had the same issue except we were plugged in using an old charger. Called support and they overnighted a new charger and cable. Solved the problem. It has been at least 6 months and no repeat of the battery indicator error issue!

Hope you get your issue solved.

Something similar happened to me two days ago. It was a repeat from 4-5 months ago.

I have a USB charger outlet in my bathroom (the kind that’s a standard AC two socket outlet with twin built in USB charges.) Every morning I check the battery level and if it’s 65% or less, I plug the pump in to charge while I’m in the shower. When I unplug from the charger (after shower, shave, etc.) it usually reads 90%-100%. The other day it read 75% but I plugged it in anyway and when I unplugged from the charger it read 5% with an alarm. I plugged it back in after turning on/off with same result.

After multiple tries, I plugged it into the supplied Tandem charger (which I seldom use). It got up to 10% followed by a message something like “pump cannot charge using this device; try another”. I ignored that because that’s what I was told to do the previous time, unplugged, and reattached to the same charger. Repeat. After the second or third time, I decided to try another charger. I went to get one, and when I unplugged from the Tandem charger to try the new one, voila: the battery indicated 100%.

I plan to call Tandem support and discuss the incident mainly because I received an email saying my pump was approaching the end of warranty and want to know what that means for future problems like this.

It Hasn’t happen to mine as far as I know, but I will certainly keep and eye out for it now Thanks


This has happened to me twice in the past 30 days. Technical support explained to me that it is a rare issue the first time I called in. The second time they said exactly what you were told, “…make it a practice to charge the pump for a few minutes every day.” I am having a hard time trusting my pump’s battery life indicator/status.
Thank you for sharing.