For a long‑haul LiPo I keep the charge‑rate in the 0.5‑1C range for the bulk phase, then drop it to 0.2‑0.3C for topping. That gives a gentle slope on the curve and keeps the cell temps in the 35‑45 °C band. I also pre‑heat the cells a bit in a warm room before charging; it evens out the chemistry and the charger doesn’t see a sudden spike. If you’re using a smart charger, set a temperature limit at 50 °C and make the charger pause when it hits that point – it keeps the curve flat. Finally, run a quick calibration with a known‑good pack before the shoot; that way the charger’s internal maps line up with reality and you avoid those nasty thermal surges.

Start the charger with a tiny pre‑charge, like 0.1C for a minute or two, then let it ramp to the bulk rate. That gives the cells a chance to equalize before the main charge. If your charger lets you tweak the ramp curve, set a slow ramp to 0.5C instead of blasting straight to 1C—those little slopes kill the mid‑charge spikes. Spot uneven cells before the flight: just put the pack on a charger set to a low 0.2C, run it for a minute, then pull it out and check each cell with a multimeter. A 50‑mV gap or more means that cell is out of line and will hit a spike later. Or better, use a quick balancer that balances all cells before you hit the road. That way your 4S stays flat and you won’t see any nasty thermal surprises.

Glad the pre‑charge idea landed. For on‑flight temp you can just stick a small thermistor on the battery case and feed it to your FPV camera’s telemetry port if you have a lightweight radio link – it adds almost no weight. Or, if your flight controller has a temperature sensor, just log that in your flight data and watch the chart in real time on the ground. The trick is to keep the sensor low‑profile and wired with a short, flexible cable so it doesn’t add drag. If you’re really light‑weight, a little 3‑D printed clip that holds a cheap temperature probe can do the trick, and you’ll get real‑time feedback without a bulk.