As technology gets smaller and more powerful, wearables and portable devices are becoming more common in our everyday lives. Makers are looking to make projects portable and with that comes the need for high capacity batteries that are reliable, powerful, and compact. The clear choice for most projects is a Lithium Polymer (also known as Lithium-ion Polymer) battery (LiPo for short).
If you haven’t already checked them out, be sure to take a look at our tutorials on using PowerBoost Modules with LiPo Batteries, and Tips for Using LiPo Batteries. They cover off on same basic safety tips and best practices when using LiPo batteries, but today we’ll be looking at what differentiates different LiPo batteries, and how to choose the best one for your project.
The first step to choosing the right LiPo is understanding the various specifications that are associated with LiPos.
- Cells: A LiPo battery is made up of cells. A cell is a bit like a smaller battery inside the pack. Each cell has a nominal voltage of 3.7V (we’ll look at cell voltage next), and while most batteries are a single cell, some can have multiple cells which is denoted by an ‘S’ which stands for ‘series’ as the cells are wired in series. Bear in mind that not all rechargeable batteries are 3.7V, this is specific to LiPo chemistry, and other types of Lithium batteries such as coin cell batteries can have a different cell voltage. For packs with multiple cells, the nominal voltage is given as 3.7 x the number of cells. So a 3S pack would be rated at 11.1V.
- Voltage: As we discussed above, a LiPo battery cell will have a nominal voltage of 3.7V. The word ‘nominal’ is used as the actual voltage of the cell will change depending on how much charge it has left. A fully charged LiPo cell will have a voltage of 4.2V, and a when it is fully depleted, a voltage of 3.0V. A quality LiPo charger will avoid overcharging your battery, however, you’ll need to monitor the voltage when in use to ensure it doesn’t drop below 3.0V otherwise you WILL damage it.
- Capacity: The capacity of a battery is usually measured in milliamp hours (or mAh for short) or just Amp hours (Ah). This is true for all batteries, not just LiPos, and 1000mAh = 1Ah. What this means is that a 1000mAh battery can deliver 1000mA (or 1 Amp) for 1 hour, before being depleted. Provided you don’t exceed the maximum discharge rating (see below), you can supply any combination of mA consumption over time to the mAh rating. To work out the power you can draw from a LiPo for any given time, use this formula:
60 x (Battery Capacity/Average Current Draw)
- Discharge Rating: All LiPo batteries are rated to provide a certain amount of current from the cell, this rating is called the discharge rating and is provided as a unit called ‘xC’. All LiPo packs will have a rating such as 1C, 2C, 10C, etc... This means that they can provide a maximum current of ‘x’ (the number in front of C), multiplied by the capacity. So a 1000mAh battery with a discharge rating of 2C can provide 2000mA (or 2A). In addition to this rating, some high-performance packs may also have a ‘burst’ discharge rating which means they can deliver a higher current for a short amount of time (we’d recommend no more than 5 seconds to be safe).
Something to take note of though is that just because the LiPo cell is rated for a certain current draw, it doesn’t mean that the connectors are. Some LiPos, particularly 1S packs have thinner leads on them to make them easier to fit into portable projects. These leads may only be rated for a 1A draw, so if you plan on using more than that, you’ll need to upgrade your pack (BE CAREFUL!!!).
- Charge Rating: The charge rating determines how quickly the battery pack can be recharged, and it’s worked out in the same way the discharge rating is. It will have a ‘C’ rating which shouldn’t be exceeded when charging (seriously, don’t do it). Whilst some batteries may feature a charge rating higher than an amp, it’s good practice to limit the charge rate of batteries to 1A to ensure safe charging and long battery life.
- Size: This one might be a little obvious, but the larger the capacity of a battery, the bigger it will be. Most LiPos are fairly thin, but always be sure to pay attention to the dimensions of your battery, lest you accidentally kneecap your project.
Now that you’ve got a handle on all of the distinguishing features of LiPo batteries, let’s compare a few different packs and look at whether they would be suitable for different projects.
All of these packs feature common specifications such as being 1S (single cell, 3.7V packs with JST connectors and 2C discharge ratings (although as mentioned above, the wiring harness is only rated for 1A). The main difference is the capacity and the physical size. So what would you use each of these packs for?
- 120mAh LiPo: These little guys are perfect for low power projects and wearables the use BLE and other low-energy consumption technologies. They pair especially well with a solar charger due to their low capacity which allows them to be quickly recharged.
- 1000mAh LiPo: 1000mAh is the sweet spot of general purpose batteries as it’s got enough juice to keep most projects running for a decent amount of time, but they’re thin enough to fit into most enclosures and cases.
- 2600mAh Cylindrical LiPo: If 1000mAh doesn’t quite cut it, and perhaps you want something less wide, then a cylindrical LiPo could be just what you're after. These guys look like a bit AA battery, but they use the same LiPo chemistry and come in two flavours, with or without solder tabs. For the version without solder tabs, we've also got both single and double battery holders specifically for these 18650 size cells.
- 6000mAh Lipo: Stepping up to the beefiest LiPo we carry, is this monster. 6000mAh is a lot of energy which is contained in a surprisingly compact package. Whilst it does away with the thin form factor of the previous packs, it’s can still fit into most medium sized projects.
So there you have it folks, our recommendations on how to choose a LiPo, some important information about the difference between different batteries, and some of our favourite packs. Bear in mind, we’ve got plenty of other packs in between those sizes, so take a look at the rest of our range, and happy making!