How to Parallel Charge

Parallel charging is quite contested in the RC community, and we regularly get our fair share of questions about it.

We've put together a great video which will hopefully answer many of your questions, and may even dispel some common misconceptions about parallel charging.  You can watch it at the bottom of this post.

First, some quick safety advice:

1.     Never mix and match different voltages!  That means never mix batteries with different cell counts.  It also means not to mix batteries with states of charge that are too different.  Before charging in parallel, check the voltage of your cells.  If your cells' voltages are 0.2V apart or less, they are ready to be connected in parallel.  If there is more of a difference than that, you will want to charge or discharge them separately.  For example, charging two batteries whose individual cell voltages are 3.6V and 3.8V would be fine, but charging a battery with cells at 3.8V with another battery whose cells are at 4.1V or greater can cause damage.

2.     Before you start, make sure all of your cables and connections are in good condition.  Check all of them, including the charger, charge cables and boards, and batteries.  If anything looks suspect, go back to charging one battery at a time and isolate variables.  Don't mix rotten apples in with your parallel apple pie!

3.     There is always some risk in charging LiPo batteries, so you should never leave your charger unattended while charging batteries.  The good news:  there is no increased risk from the proper use of parallel charging.

The main points to keep in mind when setting up your charger:

1:     The cell count of your battery does not change. For example: parallel charging two 3S batteries won't make a 6S battery. When charging multiple 3S batteries in parallel, always set up your charger as if you were charging a single 3S battery. (This goes for any cell count!)

2:     Add up the mAh of all batteries you plan on charging in parallel, and set your charger accordingly. Four 1000mAh batteries in parallel should be set to charge as if they were a single 4000mAh battery.

3:     Charging at the mAh rating listed on your battery takes one hour and is called a 1C charge rate. Many batteries can charge faster, at a 2C or even greater charge rate. Sometimes it will say on the battery what it's rated for. If not, you can check with the manufacturer online. Be sure not to mix up the discharge and charge C rating! If your battery is able to be charged at a faster charge rate, you can simply multiply the 1C charge rate by the C rating you wish to charge at, making sure not to exceed the batteries' rating. Every increase in C rating will divide the charge time by the C rating, so 2C is 1/2 as long and 3C is 1/3 as long.

4:     Do not exceed the lowest C rating of the battery packs being charged.  If you're charging a 10C capable pack in parallel with a 2C capable pack, don't go past 2C!

5:     Amperage is the current you set, which you calculate based off the combined mAh of all the packs in parallel, multiplied by the desired C charge rating that your batteries can handle. Amperage is a direct factor of the mAh * C charge rate.

Below is a handy chart if you're more of a visual learner.  In this example, parallel charging four 3S 1000mAh batteries would be set up in the charger as if charging a single 3S 4000mAh battery.

Watch the video for more details on parallel charging, and contact us if you have any questions!