I agree, solder is best.
Lipos don't loose charge when in storage and each manufactuer is different.
I had a couple of packs that where actually slightly overcharged (above 4.2 volts per cell) when I got them.
PS: never run a lipo pack empty, it can ruin the pack. Good rule of thumb is never let the pack go below 3.0 volts per cell and if your charger does not balance the cells invest in a cell balancer (an Astro Blinky is only about $25 and will help keep your lipos healthy)