Questions about battery and charging specs for capsules and vision props? How many charges you can expect from a portable USB power bank? Find your answers and more here.

Notes: The data below is approximate, and varies slightly between devices due to manufacturing tolerances and different battery conditions. 

The voltage of a li-ion battery varies from 4.2V to 3.5V during its useful capacity range. Most of its charge curve is 3.6-3.7V, and most manufacturers list them at 3.7V which we use for our calculations.

Battery and charging specs


Li-ion battery3.7V650 mAh2.4Wh
USB charging
450 mA draw3.74 Wh from usb for a full charge (~1.66 hours)

Li-ion battery 3.7V1000mAh3.7Wh
USB charging
450mA draw5.85Wh from usb for a full charge (~2.6 hours)

Notes and a quick refresher on batteries and charging:

  • V = Volts, A = Amps, mA = milliamps, W = Watts, h = hours, Wh = Watt-hours
  • mA / 1000 = A
  • V x A = W
  • W x h = Wh
  • Battery capacity: Battery voltage and capacity are listed as V and mAh, e.g. 3.7V, 1000mAh. This means the battery can output 1000mA for 1 hour, or 100mA for 10 hours, 10mA for 100h, etc. at an average of 3.7V. When accounting for power at different voltages, like 5V USB vs. 3.7V battery, or the total power of a system with multiple or variable voltage, it is useful to convert to Watt-hours (Wh). 
  • C-rating: Battery maximum current draw is listed as a ratio relative to its capacity - C. Most li-ion batteries have a rating of 1C, e.g. a 1000mAh battery can output up to 1000mA without its voltage dropping under load, generating internal heat, and reducing the lifespan of the battery. Many drone batteries have a C of 30-70 or more, enabling massive power over short periods. Flowtoys batteries are 1.5C, enabling bright pulses of light.
  • Battery chemistry changes with manufacturing conditions and their environment, and some variation in capacity and lifespan is normal. 

When is the best time to charge my battery? Should I wait until it's depleted? 

Li-ion batteries have no “memory” and do not need to be fully charged or discharged at any point, just use and charge them however is convenient for you.

80-90% of a li-ion battery charge happens fairly quickly. The last 10-20% takes much longer, then it turns off (in latest firmware). If your prop’s charge indicator is almost green (slightly yellow) then it is 80-90% charged.

How long will my battery last?

Batteries wear out over time, typically a li-ion battery will loose 1/2 its capacity or fail after about 2 years. Total use can make a difference, but they also degrade over time with no use, so use them!

Notes on charging circuit and power loss

USB power banks lose 10-20% of their power as heat converting 3.7V to 5V USB power.

The li-ion charging circuit loses about 35% of its power as heat, converting 5V USB power to 3.7V and pushing it into the battery.

The charging circuit used in vision and capsule lights is by far the most common in small electronic devices. It uses a simple liner regulator, dropping the USB power from 5V down to the battery voltage of ~3.7V by converting the excess to heat. It is compact, durable, economical, and fast, but it is not very efficient. These devices use so little power that the low efficiency rarely matters. If you are charging many of them off a portable battery bank or micro solar/off-grid system, this inefficiency might effect you, but the alternative is a switching regulator that requires many more fragile components, a lot of space on the PCB, and much more cost. It simply could not fit on a capsule, and would not be worth the trade-off in vision props.

Charging multiple props from a single USB port or hub:

  • If you want to charge more things from a single USB port, you can use a powered hub with enough total power, or a non-powered USB hub, as long as you do not exceed the total power output of the USB power source (computer or wall adaptor).
  • Each light draws 450mA when charging - a 1A port can charge 2 lights, a 2A port can charge 4 lights at once. 
  • The maximum power output of a single USB port is often shared amongst both ports, so even if one is labeled 2A and the other is 1A, you might not get 3A total.
  • We have found that non-powered 4-port hubs will work well to charge flowtoys off most computers and many wall-adaptors.

USB power-banks/off-grid charging:

  • Power banks are often overrated, and also list their battery capacity at 3.7v instead of the output of 5v, so make sure to calculate your actual Wh (W=V*A) and consider if you trust your source. If it looks too good to be true, it probably is!
  • Typically 10-20% of power is lost in converting from the 3.7V battery to 5V USB.
  • 80-90% of a li-ion battery charge happens fairly quickly - the last 10-20% takes much longer, then it turns off (in latest firmware).
  • If your prop’s charge indicator is almost green (slightly yellow) then it is 80-90% charged, and you may want to unplug it at this point to maximize power savings.
  • Most power banks turn off automatically after your flowtoys are done charging and have stopped drawing power, but some do not and might continue to drain after charging. You can test if yours turns off automatically after charging, and/or unplug them once they are breathing green.

Flowtoys USB power banks comes with 2 x 3.7V 2600mAh batteries for a total of 19.24Wh of power

  • a vision prop battery uses 5.85Wh for a full charge. 16/5.85 = 2.73 full charges
  • a capsule battery uses 3.74Wh for a full charge. 16/3.74 = 4.28 full charges

DIY battery replacement:

If you are interested in soldering in a replacement battery yourself, contact us.

If you would like to try using a battery other than flowtoys custom-built super-durable batteries, we love to support DIY solutions and it won’t void your warranty. Here are some tips:

  • the voltage can be anything between 3.6-4.2V 
  • the mAh only effects the runtime --> more is more.
  • the battery wires must be durable to handle frequent flexing on impact. They are also pone to breaking at the solder joints - strain-relief, like thick flexible glue, is recommended. Taking the wires off your old flowtoys battery and using them is also recommended.
  • it is possible a low quality, specialty, or too-small battery or wire cannot handle the current draw of the brightest modes (~600mA), causing the light to turn off.
  • the inner construction of most cylindrical li-ion cells cannot handle much use as poi and may break easily, internally. flowtoys custom battery and custom high-flex wire are highly recommended, especially if the work of replacing the battery often is not convenient for you.