Most lithium cell manufacturers recommended charge voltage of 14.2 - 14.6V (for four cells), 13.8 will charge them but not as fast or fully. If you do not go high enough, the BMS will not work properly (as most of the small ones are top balancing). The longevity tests I've seen suggest 14.2V as the best compromise. I've been using this charger:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

It can be set for proper voltages for LFP, SLA, flooded, or pretty much anything. It is a true connect and forget charger, with correct float voltages for any chemistry including lithium. Like the Powersonic battery, there is a free phone app (somewhat better than Powersonic's) that connects with Bluetooth, delivers status and history and allows wide configuration of all parameters, though it can be operated very simply with the one button on the top. It's default LFP program is 14.2V CC charge, and 13.5V float (effectively disconnected) which is perfect. A bit more than a $20 Chinese charger, but it is less likely to burn your house down .

The BMS will disconnect if the high charge voltage is exceeded, but that is pretty high on the Powersonic (15.2V according to their spec). You really should not depend on this routinely, hard on the cells.

Another point to remember about lithium is that unlike SLA, they like to be operated and stored in the middle of the charge range. On the last flight of the weekend I do not recharge (it will be about 50% SOC), leave it that way until I am going to fly again. With the above charger, I normally charge at the 2A setting, but you can run it at 5A for a quicker charge (in the morning when you have forgotten to charge it!). The battery will accept it, a bit harder on it maybe but it is OK to do when needed. LFP will charge at full current until about 95% SOC.

SLA batteries need to be charged fully immediately after use, and stored that way or they will die early.

On Monday, September 14, 2020 at 8:36:35 AM UTC-7, wrote:
Jfitch,

What are you using to charge it? The manufacturer seems to recommend an ordinary 13.8 volt switching power supply which makes sense with the BMS handling the rest of the work