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Weaker power when battery gets low(thin)

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I have had my Sondors Thin for about a year now & use it daily to get to work/home.  I started noticing the bike was having trouble staying at full speed when the battery was running low a few months ago, it would keep me running at 19 instead of the full 20 when the battery was at about a quarter charge left(one bar on the screens battery indicator).  Since then it has gotten progressively worse and is now down to only holding me at 16 with a low battery, when the battery is full the bike performs like it did straight out of the box but only for the first quarter of the battery or so.  I have kept the bike factory except for the tires & inner tubes, I am running tubeless on the front & the standard setup on the rear at the moment, doesn't seem relevant but was advised to list any mods.  I am wondering if anyone can point me in the right direction for troubleshooting this problem, I am thinking it is the controller going bad because I have taken proper care of my battery per the instructions that came with my Sondors & the fact that it performs perfectly fine when the battery is full but I would like to get some other opinions on the matter before I start replacing/upgrading anything.  

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It would help if I knew a little more about your usage. How many total  miles do you now have on your Thin? How far do you ride each day to work and back. Do you recharge at work for your return trip? You say 1/4 charge or 1 bar on the battery screen so I gather you have the Sondors LCD and have the stock Thin 36Volt 8.7ah battery? What PAS setting do you use to ride at 20 mph or do you just use throttle?  Phoenix ain't flat so are there many hills on your route?  Your tires won't be an issue unless they are under inflated and since your running tubless in front I assume you keep them properly inflated. 

The LCD battery indicator is a poor indicator of actual battery usage. You are correct to assume that ts a general indicator of reserve but it's notoriously inaccurate. The Volt reading on screen 3 (I believe it is) is the true measure. As a matter of energy, the battery supplies to the motor, the voltage will determine the speed you will travel. The higher the voltage the faster you will go and as voltage drops (the longer you ride, the lower the voltage drops) the slower you will go.

i doubt you have a controller problem but I'd suspect the battery is just losing capacity over time. The best practice, to keep up battery capacity is to ride to conserve as much as you can. That means using the throttle as conservatively as possible and at the lowest PAS setting to achieve the desired range and velocity. If you just jamb the throttle full from every stop you'll drain capacity faster than judiciously applying power with throttle or not using it at all.

Since the stock Thin Triangle Battery Is the lowest capacity in the fleet and you report you pretty much ride at balls to the wall, it just that you are seeing reduced capacity from an aging battery. If you can't live with it, you can consider a much better battery, for increased performance from one of the 3 Sondors after market suppliers, or, use the opportunity to switch to the higher capacity and voltage battery, higher amperage controller and required compatible LCD combo (stock Sondors LCD will not work with any aftermarket controller) and increase performance exponentially.




Further you might want to read: https://tinyurl.com/ReddysGuideToBatteries






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Thanks for replying.  I have a little over 2800 miles on my bike.  I ride a little over 5 miles one way to work and sometimes charge it at work if I forget to charge it the night before.  I do have the LCD with the 36v 8.7ah battery.  When I use the PAS I usually keep it on 1 otherwise it forces me to pedal faster than I prefer to but my concern is when I am using only the throttle. I normally try to ride unassisted at least partly in the morning to justify being lazy after work & using the throttle.  I will have to check out the voltage reading while I am riding this week & I will check out the links you have provided. 

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Roger That, and when you check the voltage on the LCD, check while coasting, less you'll be reading during voltage sag not the batteries actual voltage because of demand from pedaling or throttle. 

Your 36v battery should charge to 42v when new and fully charged. Because it's a year old it's normal for it to charge to a lower voltage and stabilizes/balances, even lower over night. Heat is the enemy of Li Ion batteries and charging and discharging (which raises battery cell temperature) is exacerbated in hot enviroments. Our batteries charge, discharge and last longer at about 40°f. 

Ive flown my aircraft in to several airports in Phoenix on trips from Texas to San Francisco and you guys probably have the highest average mean temperatures in the US except for Death Valley. The stock 2amp chargers shouldn't raise temps too high but a good practice would be to wait for a period, for the battery to cool some after riding and then charge the battery inside a cool environment. That said, its just best practice and not recorded how much can be gained or lost from doing or not. 



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